Fix LocalAdapter.deliver/2 return type (#589)

Fix the `LocalAdapter.deliver/2` to return a `{:ok, result}` tuple when
the adapter is configured with the `open_email_in_browser_url` option.

lib/bamboo/adapters/local_adapter.ex

@@ -33,7 +33,8 @@ defmodule Bamboo.LocalAdapter do
   @doc "Adds email to `Bamboo.SentEmail`, can automatically open it in new browser tab"
   def deliver(email, %{open_email_in_browser_url: open_email_in_browser_url}) do
     %{private: %{local_adapter_id: local_adapter_id}} = SentEmail.push(email)
-    open_url_in_browser("#{open_email_in_browser_url}/#{local_adapter_id}")
+
+    {:ok, open_url_in_browser("#{open_email_in_browser_url}/#{local_adapter_id}")}
   end
 
   def deliver(email, _config) do