Mitigate the warnings by adding step -1

```
warning: 100..0 has a default step of -1, please write 100..0//-1 instead
  test/elixir/test/view_pagination_test.exs:62: ViewPaginationTest."test descending view pagination"/1

Running ExUnit with seed: 709278, max_cases: 1
Excluding tags: [:"test/elixir/test/config/skip.elixir", :pending]
Including tags: [:"test/elixir/test/config/suite.elixir"]

warning: 14..-1 has a default step of -1, please write 14..-1//-1 instead
  test/elixir/test/uuids_test.exs:91: UUIDsTest."test utc_id uuids are correct"/1
```

Author: jiahuili430

test/elixir/test/uuids_test.exs

@@ -88,7 +88,7 @@ defmodule UUIDsTest do
 
     Enum.reduce(resp.body["uuids"], fn curr, acc ->
       assert String.length(curr) == 14 + String.length(@utc_id_suffix)
-      assert String.slice(curr, 14..-1) == @utc_id_suffix
+      assert String.slice(curr, 14..-1//-1) == @utc_id_suffix
       assert curr > acc
       curr
     end)

test/elixir/test/view_pagination_test.exs

@@ -59,7 +59,7 @@ defmodule ViewPaginationTest do
 
     query_function = "function(doc) { emit(doc.integer, null); }"
 
-    100..0
+    100..0//-1
     |> Enum.filter(fn number -> rem(number, 10) === 0 end)
     |> Enum.map(&(&1 - 1))
     |> Enum.filter(&(&1 > 0))