Fix AM testcase break with mail 2.5.4. It seems that AM's testcase was wrong.

actionmailer/CHANGELOG.md

-* No changes.
+* Fix ActionMailer testcase break with mail 2.5.4.
+  ActionMailer's testcase was wrong, because :transfer_encoding option was ignored in mail 2.5.3.
+
+  *kennyj*
 
 Please check [4-0-stable](https://github.com/rails/rails/blob/4-0-stable/actionmailer/CHANGELOG.md) for previous changes.

actionmailer/test/mailers/base_mailer.rb

@@ -38,7 +38,7 @@ def attachment_with_content(hash = {})
   end
 
   def attachment_with_hash
-    attachments['invoice.jpg'] = { data: "\312\213\254\232)b",
+    attachments['invoice.jpg'] = { data: ::Base64.encode64("\312\213\254\232)b"),
                                    mime_type: "image/x-jpg",
                                    transfer_encoding: "base64" }
     mail