Revert "Bump up mail dependency to take advantage of relaxed i18n version requirement"

Locking to ~> 2.2.9.1 means locking to < 2.2.10, not intended behaviour.

This reverts commit e7de5dd1.

actionmailer/actionmailer.gemspec

@@ -20,5 +20,5 @@
   s.has_rdoc = true
 
   s.add_dependency('actionpack',  version)
-  s.add_dependency('mail',        '~> 2.2.9.1')
+  s.add_dependency('mail',        '~> 2.2.9')
 end