add Gemfile

[pille]

after upgrading to chiliproject-2.1.1 migrations fail, because chiliproject now uses bundler and breaks on missing gems.
plugins should add a Gemfile with their needs: https://www.chiliproject.org/issues/529#note-3

i created vendor/plugins/redmine_airbrake_server/Gemfile as to fix this:

gem "hpricot"

[milgner]

Thanks for the hint. I'm still struggling with properly setting up my CI to host a Redmine installation wherein I can automatically test my plugins. As soon as I figure out how to do this, I will set up a ChiliProject instance, too.