drop ruby 1.9.2, add latest stable

Ruby 1.9.2 is EOL, and 1.9.3 is not far behind. Foodcritic 4.x requires
at least 1.9.3. This currently blocks travis tests from completing on 1.9.2

Ref: https://github.com/acrmp/foodcritic/commit/9c312ca2113dfd0185f0dbcd3e7d9a6a32d0bf99