Approximate master/production libs from master Gemfile.lock. 

- The Gemfile copies the versions from master branch Gemfile.lock, only for the gems listed in the master Gemfile, not each gems sub-dependencies..

- A matching Gemfile and Gemfile.lock are required to build with --production, which is travis default if it finds a Gemfile.lock.

- Also downgrade system gems to 2.1 in .travis.yml file and add debugger to preinstall, but again, production may be different.