add Ruby 1.9.2 to .travis.yml

git-svn-id: http://svn.redmine.org/redmine@13354 e93f8b46-1217-0410-a6f0-8f06a7374b81
Merged r13354 from trunk to 2.5-stable

add Ruby 1.9.2 to .travis.yml

git-svn-id: http://svn.redmine.org/redmine@13355 e93f8b46-1217-0410-a6f0-8f06a7374b81