Use explicit steps to remove 1.16 deprecation warning (#322)

lib/excoveralls/cobertura.ex

@@ -173,7 +173,7 @@ defmodule ExCoveralls.Cobertura do
     c_paths
     |> Enum.find_value(package_name, fn c_path ->
       if String.starts_with?(package_name, c_path) do
-        String.slice(package_name, (String.length(c_path) + 1)..-1)
+        String.slice(package_name, get_slice_range_for_package_name(c_path))
       else
         false
       end
@@ -183,6 +183,14 @@ defmodule ExCoveralls.Cobertura do
     |> to_charlist()
   end
 
+  # TODO: Remove when we require Elixir 1.12 as minimum and inline it with range syntax
+  if Version.match?(System.version(), ">= 1.12.0") do
+    # We use Range.new/3 because using x..y//step would give a syntax error on Elixir < 1.12
+    defp get_slice_range_for_package_name(c_path), do: Range.new(String.length(c_path) + 1, -1, 1)
+  else
+    defp get_slice_range_for_package_name(c_path), do: (String.length(c_path) + 1)..-1
+  end
+
   defp rate(valid_lines) when length(valid_lines) == 0, do: 0.0
 
   defp rate(valid_lines) do