Use charlist sigil to avoid warnings in recent Elixir. (#130)

* Replace non-interpolation ~c sigils with ~C

---------

Co-authored-by: Andrew Bruce <[email protected]>
Co-authored-by: Sergey Fedorov <[email protected]>

lib/avrora/http_client.ex

@@ -12,7 +12,7 @@ defmodule Avrora.HTTPClient do
   def get(url, options \\ []) do
     with {:ok, headers} <- extract_headers(options),
          {:ok, ssl_options} <- extract_ssl(options),
-         {:ok, {{_, status, _}, _, body}} <- :httpc.request(:get, {'#{url}', headers}, [ssl: ssl_options], []) do
+         {:ok, {{_, status, _}, _, body}} <- :httpc.request(:get, {~c(#{url}), headers}, [ssl: ssl_options], []) do
       handle(status, body)
     end
   end
@@ -25,7 +25,7 @@ defmodule Avrora.HTTPClient do
          {:ok, headers} <- extract_headers(options),
          {:ok, ssl_options} <- extract_ssl(options),
          {:ok, {{_, status, _}, _, body}} <-
-           :httpc.request(:post, {'#{url}', headers, [content_type], body}, [ssl: ssl_options], []) do
+           :httpc.request(:post, {~c(#{url}), headers, [content_type], body}, [ssl: ssl_options], []) do
       handle(status, body)
     end
   end
@@ -34,12 +34,12 @@ defmodule Avrora.HTTPClient do
     authorization =
       case Keyword.get(options, :authorization) do
         nil -> []
-        credentials -> [{'Authorization', '#{credentials}'}]
+        credentials -> [{~C(Authorization), ~c(#{credentials})}]
       end
 
     case Keyword.get(options, :user_agent) do
       nil -> {:ok, authorization}
-      user_agent -> {:ok, [{'User-Agent', '#{user_agent}'} | authorization]}
+      user_agent -> {:ok, [{~C(User-Agent), ~c(#{user_agent})} | authorization]}
     end
   end