diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 5d8d102..895f3c5 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -8,18 +8,21 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        otp: ['20.3']
-        elixir: ['1.4', '1.5', '1.6', '1.7']
+        include:
+          - otp: '21.3'
+            elixir: '1.11'
+          - otp: '26.0'
+            elixir: '1.15'
     env:
       MIX_ENV: test
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: erlef/setup-beam@v1
         with:
          otp-version: ${{ matrix.otp }}
          elixir-version: ${{ matrix.elixir }}
-      - uses: actions/cache@v2
+      - uses: actions/cache@v3
         with:
          path: deps
          key: ${{ runner.os }}-mix-${{ hashFiles(format('{0}{1}', github.workspace, '/mix.lock')) }}
diff --git a/lib/excoveralls/cover.ex b/lib/excoveralls/cover.ex
index f444eaa..a0d3550 100644
--- a/lib/excoveralls/cover.ex
+++ b/lib/excoveralls/cover.ex
@@ -14,7 +14,9 @@ defmodule ExCoveralls.Cover do
     {:ok, string_io} = StringIO.open("")
     Process.group_leader(pid, string_io)
 
-    :cover.compile_beam_directory(compile_path |> string_to_charlist)
+    compile_path
+    |> String.to_charlist()
+    |> :cover.compile_beam_directory()
   end
 
   @doc """
@@ -59,12 +61,6 @@ defmodule ExCoveralls.Cover do
     :cover.analyse(module, :calls, :line)
   end
 
-  if Version.compare(System.version, "1.3.0") == :lt do
-    defp string_to_charlist(string), do: String.to_char_list(string)
-  else
-    defp string_to_charlist(string), do: String.to_charlist(string)
-  end
-
   defp file_exist?(module, path) do
     if File.exists?(path) do
       true
diff --git a/mix.exs b/mix.exs
index 267835b..72c6b33 100644
--- a/mix.exs
+++ b/mix.exs
@@ -7,7 +7,7 @@ defmodule ExCoveralls.Mixfile do
     [
       app: :excoveralls,
       version: "0.16.1",
-      elixir: "~> 1.3",
+      elixir: "~> 1.11",
       elixirc_paths: elixirc_paths(Mix.env()),
       deps: deps(),
       docs: docs(),
diff --git a/mix.lock b/mix.lock
index 6b7d7a4..ee61118 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,10 +1,10 @@
 %{
-  "certifi": {:hex, :certifi, "2.5.2", "b7cfeae9d2ed395695dd8201c57a2d019c0c43ecaf8b8bcb9320b40d6662f340", [:rebar3], [{:parse_trans, "~>3.3", [hex: :parse_trans, repo: "hexpm", optional: false]}], "hexpm", "3b3b5f36493004ac3455966991eaf6e768ce9884693d9968055aeeeb1e575040"},
+  "certifi": {:hex, :certifi, "2.9.0", "6f2a475689dd47f19fb74334859d460a2dc4e3252a3324bd2111b8f0429e7e21", [:rebar3], [], "hexpm", "266da46bdb06d6c6d35fde799bcb28d36d985d424ad7c08b5bb48f5b5cdd4641"},
   "earmark": {:hex, :earmark, "1.4.3", "364ca2e9710f6bff494117dbbd53880d84bebb692dafc3a78eb50aa3183f2bfd", [:mix], [], "hexpm", "8cf8a291ebf1c7b9539e3cddb19e9cef066c2441b1640f13c34c1d3cfc825fec"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.12", "b245e875ec0a311a342320da0551da407d9d2b65d98f7a9597ae078615af3449", [:mix], [], "hexpm", "711e2cc4d64abb7d566d43f54b78f7dc129308a63bc103fbd88550d2174b3160"},
   "ex_doc": {:hex, :ex_doc, "0.23.0", "a069bc9b0bf8efe323ecde8c0d62afc13d308b1fa3d228b65bca5cf8703a529d", [:mix], [{:earmark_parser, "~> 1.4.0", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}], "hexpm", "f5e2c4702468b2fd11b10d39416ddadd2fcdd173ba2a0285ebd92c39827a5a16"},
-  "hackney": {:hex, :hackney, "1.16.0", "5096ac8e823e3a441477b2d187e30dd3fff1a82991a806b2003845ce72ce2d84", [:rebar3], [{:certifi, "2.5.2", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "6.0.1", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~>1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.3.0", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.6", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm", "3bf0bebbd5d3092a3543b783bf065165fa5d3ad4b899b836810e513064134e18"},
-  "idna": {:hex, :idna, "6.0.1", "1d038fb2e7668ce41fbf681d2c45902e52b3cb9e9c77b55334353b222c2ee50c", [:rebar3], [{:unicode_util_compat, "0.5.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "a02c8a1c4fd601215bb0b0324c8a6986749f807ce35f25449ec9e69758708122"},
+  "hackney": {:hex, :hackney, "1.18.1", "f48bf88f521f2a229fc7bae88cf4f85adc9cd9bcf23b5dc8eb6a1788c662c4f6", [:rebar3], [{:certifi, "~> 2.9.0", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "~> 6.1.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "~> 1.0.0", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~> 1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.3.1", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "~> 1.1.0", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}, {:unicode_util_compat, "~> 0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "a4ecdaff44297e9b5894ae499e9a070ea1888c84afdd1fd9b7b2bc384950128e"},
+  "idna": {:hex, :idna, "6.1.1", "8a63070e9f7d0c62eb9d9fcb360a7de382448200fbbd1b106cc96d3d8099df8d", [:rebar3], [{:unicode_util_compat, "~> 0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "92376eb7894412ed19ac475e4a86f7b413c1b9fbb5bd16dccd57934157944cea"},
   "jason": {:hex, :jason, "1.1.1", "d3ccb840dfb06f2f90a6d335b536dd074db748b3e7f5b11ab61d239506585eb2", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "639645cfac325e34938167b272bae0791fea3a34cf32c29525abf1d323ed4c18"},
   "makeup": {:hex, :makeup, "1.0.5", "d5a830bc42c9800ce07dd97fa94669dfb93d3bf5fcf6ea7a0c67b2e0e4a7f26c", [:mix], [{:nimble_parsec, "~> 0.5 or ~> 1.0", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "cfa158c02d3f5c0c665d0af11512fed3fba0144cf1aadee0f2ce17747fba2ca9"},
   "makeup_elixir": {:hex, :makeup_elixir, "0.15.0", "98312c9f0d3730fde4049985a1105da5155bfe5c11e47bdc7406d88e01e4219b", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}, {:nimble_parsec, "~> 1.1", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "75ffa34ab1056b7e24844c90bfc62aaf6f3a37a15faa76b07bc5eba27e4a8b4a"},
@@ -13,9 +13,9 @@
   "mimerl": {:hex, :mimerl, "1.2.0", "67e2d3f571088d5cfd3e550c383094b47159f3eee8ffa08e64106cdf5e981be3", [:rebar3], [], "hexpm", "f278585650aa581986264638ebf698f8bb19df297f66ad91b18910dfc6e19323"},
   "mock": {:hex, :mock, "0.3.6", "e810a91fabc7adf63ab5fdbec5d9d3b492413b8cda5131a2a8aa34b4185eb9b4", [:mix], [{:meck, "~> 0.8.13", [hex: :meck, repo: "hexpm", optional: false]}], "hexpm", "bcf1d0a6826fb5aee01bae3d74474669a3fa8b2df274d094af54a25266a1ebd2"},
   "nimble_parsec": {:hex, :nimble_parsec, "1.1.0", "3a6fca1550363552e54c216debb6a9e95bd8d32348938e13de5eda962c0d7f89", [:mix], [], "hexpm", "08eb32d66b706e913ff748f11694b17981c0b04a33ef470e33e11b3d3ac8f54b"},
-  "parse_trans": {:hex, :parse_trans, "3.3.0", "09765507a3c7590a784615cfd421d101aec25098d50b89d7aa1d66646bc571c1", [:rebar3], [], "hexpm", "17ef63abde837ad30680ea7f857dd9e7ced9476cdd7b0394432af4bfc241b960"},
+  "parse_trans": {:hex, :parse_trans, "3.3.1", "16328ab840cc09919bd10dab29e431da3af9e9e7e7e6f0089dd5a2d2820011d8", [:rebar3], [], "hexpm", "07cd9577885f56362d414e8c4c4e6bdf10d43a8767abb92d24cbe8b24c54888b"},
   "sax_map": {:hex, :sax_map, "1.0.1", "51a9382d741504c34d49118fb36d691c303d042e1da88f8edae8ebe75fe74435", [:mix], [{:saxy, "~> 1.0", [hex: :saxy, repo: "hexpm", optional: false]}], "hexpm", "a7c57c25d23bfc3ce93cf93400dcfb447fe463d27ee8c6913545161e78dc487a"},
   "saxy": {:hex, :saxy, "0.10.0", "38879f46a595862c22114792c71379355ecfcfa0f713b1cfcc59e1d4127f1f55", [:mix], [], "hexpm", "da130ed576e9f53d1a986ec5bd2fa72c1599501ede7d7a2dceb81acf53bf9790"},
-  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.6", "cf344f5692c82d2cd7554f5ec8fd961548d4fd09e7d22f5b62482e5aeaebd4b0", [:make, :mix, :rebar3], [], "hexpm", "bdb0d2471f453c88ff3908e7686f86f9be327d065cc1ec16fa4540197ea04680"},
-  "unicode_util_compat": {:hex, :unicode_util_compat, "0.5.0", "8516502659002cec19e244ebd90d312183064be95025a319a6c7e89f4bccd65b", [:rebar3], [], "hexpm", "d48d002e15f5cc105a696cf2f1bbb3fc72b4b770a184d8420c8db20da2674b38"},
+  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.7", "354c321cf377240c7b8716899e182ce4890c5938111a1296add3ec74cf1715df", [:make, :mix, :rebar3], [], "hexpm", "fe4c190e8f37401d30167c8c405eda19469f34577987c76dde613e838bbc67f8"},
+  "unicode_util_compat": {:hex, :unicode_util_compat, "0.7.0", "bc84380c9ab48177092f43ac89e4dfa2c6d62b40b8bd132b1059ecc7232f9a78", [:rebar3], [], "hexpm", "25eee6d67df61960cf6a794239566599b09e17e668d3700247bc498638152521"},
 }
diff --git a/test/json_test.exs b/test/json_test.exs
index b129281..d384870 100644
--- a/test/json_test.exs
+++ b/test/json_test.exs
@@ -34,7 +34,7 @@ defmodule ExCoveralls.JsonTest do
         File.rm!(path)
         File.rmdir!(@test_output_dir)
       end
-      
+
       ExCoveralls.ConfServer.clear()
     end
 
@@ -53,7 +53,16 @@ defmodule ExCoveralls.JsonTest do
       Json.execute(@source_info)
     end) =~ @stats_result
 
-    assert(File.read!(report) =~ ~s({"source_files":[{"coverage":[0,1,null,null],"name":"test/fixtures/test.ex","source":"defmodule Test do\\n  def test do\\n  end\\nend\\n"}]}))
+    assert(
+      %{
+        "source_files" => [
+          %{
+            "coverage" => [0, 1, nil, nil],
+            "name" => "test/fixtures/test.ex",
+            "source" => "defmodule Test do\n  def test do\n  end\nend\n"
+          }
+        ]
+      } = Jason.decode!(File.read!(report)))
     %{size: size} = File.stat! report
     assert(size == @file_size)
   end
@@ -63,7 +72,16 @@ defmodule ExCoveralls.JsonTest do
       Json.execute(@source_info, [output_dir: @test_output_dir])
     end) =~ @stats_result
 
-    assert(File.read!(report) =~ ~s({"source_files":[{"coverage":[0,1,null,null],"name":"test/fixtures/test.ex","source":"defmodule Test do\\n  def test do\\n  end\\nend\\n"}]}))
+    assert(
+      %{
+        "source_files" => [
+          %{
+            "coverage" => [0, 1, nil, nil],
+            "name" => "test/fixtures/test.ex",
+            "source" => "defmodule Test do\n  def test do\n  end\nend\n"
+          }
+        ]
+      } = Jason.decode!(File.read!(report)))
     %{size: size} = File.stat! report
     assert(size == @file_size)
   end
diff --git a/test/post_test.exs b/test/post_test.exs
index 810ca75..fd62b8e 100644
--- a/test/post_test.exs
+++ b/test/post_test.exs
@@ -34,15 +34,23 @@ defmodule ExCoveralls.PostTest do
         flagname: "arbitrary_value"
       ])
 
-    assert json ==
-      "{\"flag_name\":\"arbitrary_value\",\"git\":{\"branch\":\"\",\"head\":{\"committer_name\":\"\",\"id\":\"\",\"message\":\"\"}}," <>
-         "\"parallel\":null," <>
-         "\"repo_token\":\"1234567890\"," <>
-         "\"service_name\":\"local\"," <>
-         "\"service_number\":\"build_num_1\"," <>
-         "\"source_files\":" <>
-           "[{\"coverage\":[0,1,null,null]," <>
-             "\"name\":\"test/fixtures/test.ex\"," <>
-             "\"source\":\"defmodule Test do\\n  def test do\\n  end\\nend\\n\"}]}"
+    assert Jason.decode!(json) == %{
+      "flag_name" => "arbitrary_value",
+      "git" => %{
+        "branch" => "",
+        "head" => %{"committer_name" => "", "id" => "", "message" => ""}
+      },
+      "parallel" => nil,
+      "repo_token" => "1234567890",
+      "service_name" => "local",
+      "service_number" => "build_num_1",
+      "source_files" => [
+        %{
+          "coverage" => [0, 1, nil, nil],
+          "name" => "test/fixtures/test.ex",
+          "source" => "defmodule Test do\n  def test do\n  end\nend\n"
+        }
+      ]
+    }
   end
 end