Drop dialyxir to stable version

Attempts to publish to Hex were thwarted by having a "pre-release"
dependency.

mix.exs

@@ -37,7 +37,7 @@ defmodule Harald.MixProject do
     [
       {:circuits_uart, "~> 1.3"},
       {:credo, "~> 1.0", runtime: false},
-      {:dialyxir, "1.0.0-rc.4", runtime: false},
+      {:dialyxir, "0.5.1", runtime: false},
       {:ex_doc, "~> 0.19", only: [:dev], runtime: false},
       {:excoveralls, "~> 0.10", only: [:test], runtime: false},
       {:mix_test_watch, "~> 0.9", only: [:dev], runtime: false},

mix.lock

@@ -3,7 +3,7 @@
   "certifi": {:hex, :certifi, "2.4.2", "75424ff0f3baaccfd34b1214184b6ef616d89e420b258bb0a5ea7d7bc628f7f0", [:rebar3], [{:parse_trans, "~>3.3", [hex: :parse_trans, repo: "hexpm", optional: false]}], "hexpm"},
   "circuits_uart": {:hex, :circuits_uart, "1.3.0", "a489e648f358fb3c59e8dd146ead4295cec09d8abae3a0024be2fe3a0b6ddf8b", [:mix], [{:elixir_make, "~> 0.4", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm"},
   "credo": {:hex, :credo, "1.0.0", "aaa40fdd0543a0cf8080e8c5949d8c25f0a24e4fc8c1d83d06c388f5e5e0ea42", [:mix], [{:bunt, "~> 0.2.0", [hex: :bunt, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm"},
-  "dialyxir": {:hex, :dialyxir, "1.0.0-rc.4", "71b42f5ee1b7628f3e3a6565f4617dfb02d127a0499ab3e72750455e986df001", [:mix], [{:erlex, "~> 0.1", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm"},
+  "dialyxir": {:hex, :dialyxir, "0.5.1", "b331b091720fd93e878137add264bac4f644e1ddae07a70bf7062c7862c4b952", [:mix], [], "hexpm"},
   "earmark": {:hex, :earmark, "1.3.1", "73812f447f7a42358d3ba79283cfa3075a7580a3a2ed457616d6517ac3738cb9", [:mix], [], "hexpm"},
   "elixir_make": {:hex, :elixir_make, "0.4.2", "332c649d08c18bc1ecc73b1befc68c647136de4f340b548844efc796405743bf", [:mix], [], "hexpm"},
   "erlex": {:hex, :erlex, "0.1.6", "c01c889363168d3fdd23f4211647d8a34c0f9a21ec726762312e08e083f3d47e", [:mix], [], "hexpm"},