Merged r12172 from trunk to 2.3-stable (#14883)

Gemfile: update jdbc adapter version above 1.2.6.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/branches/2.3-stable@12174 e93f8b46-1217-0410-a6f0-8f06a7374b81