Use assert_dom_equal

Order of attribute is not specified(why? I don't know yet),
so I use assert_dom_equal
(implimented in actionpack/lib/action_dispatch/testing/assertions/dom.rb)
Use assert_dom_equal in failed test against rails4
Merge pull request #42 from sanemat/feature/assert-dom-equal

Use assert_dom_equal instead of assert_equal