Fix code readability issues

lib/service/email_checker.ex

@@ -1,15 +1,14 @@
 defmodule Mobilizon.Service.EmailChecker do
   @moduledoc """
-  Provides a function to test emails against a "not so bad" regex
+  Provides a function to test emails against a "not so bad" regex.
   """
 
+  # TODO: simplify me!
   @email_regex ~r/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/
 
   @doc """
-  Returns whether the email is valid
+  Returns whether the email is valid.
   """
-  @spec valid?(String.t()) :: boolean()
-  def valid?(email) do
-    email =~ @email_regex
-  end
+  @spec valid?(String.t()) :: boolean
+  def valid?(email), do: email =~ @email_regex
 end