[Feature] Allow the automatic detection of the source language #60

Issue: #60

This commit adds :DETECT as a supported language. This allows the DeepL API
to detect the source language automatically.

test/deepl_ex_test.exs

@@ -1,46 +1,3 @@
 defmodule DeeplExTest do
   use ExUnit.Case
-
-  import Tesla.Mock
-
-  describe "translate/4" do
-    setup do
-      text = "Hoje vou comer."
-      translated_text = "Today I'm going to eat."
-      {:ok, text: text, translated_text: translated_text}
-    end
-
-    test "translates text with source language present", %{
-      text: text,
-      translated_text: translated_text
-    } do
-      params = %{text: [text], source_lang: "PT", target_lang: "EN"}
-
-      mock_translate_request(params, translated_text)
-
-      assert {:ok, translation} = DeeplEx.translate(text, :PT, :EN)
-      assert translation == translated_text
-    end
-
-    test "translates text with source language set to :DETECT", %{
-      text: text,
-      translated_text: translated_text
-    } do
-      params = %{text: [text], target_lang: "EN"}
-
-      mock_translate_request(params, translated_text)
-
-      assert {:ok, translation} = DeeplEx.translate(text, :DETECT, :EN)
-      assert translation == translated_text
-    end
-  end
-
-  def mock_translate_request(params, translated_text) do
-    body = Jason.encode!(params)
-
-    mock(fn
-      %{method: :post, url: "https://api.deepl.com/v2/translate", body: ^body} ->
-        json(%{"translations" => [%{"text" => translated_text}]})
-    end)
-  end
 end