rails/rails — pull request #10646 by kennyj (2013-05-16 16:01:12+00:00)
Title: Fix AM testcase break introduced since mail 2.5.4.

According to https://travis-ci.org/rails/rails/jobs/7220308#L148, AM's testcase was break.
It seems that AM's testcase was wrong. And default encoding in ruby2.0.0 is utf-8.