Merged r13037 from trunk to 2.4-stable

replace mail options reference URL at configuration.yml.example.

wiki.rubyonrails.org seems dead.

git-svn-id: http://svn.redmine.org/redmine/branches/2.4-stable@13039 e93f8b46-1217-0410-a6f0-8f06a7374b81