Removing the auto usage of older Ruby.

Chef ecosystem seems fine with latest Ruby versions now so there is no
need to stick with using 1.9.3
Bump gems
Test-Kitchen should use latest stable Debian.
This seems to have sneaked in, should never have been committed.
Adding test for ruby-install version bump.
Should build/test latest Rubies.
Fixing Debian version for test-kitchen
Fixing ownership of ruby-install binary in Debian
Fixing Rubocop warnings. Incress max lines length to 99
Make Rubocop a bit more leniant with method lengths
Refactor long method into two.
Adding some extra docs about contributing.