Ruby 2.2 Dockerfiles

Based on the 2.1 Dockerfiles, changing only env vars
Merge branch 'master' of https://github.com/docker-library/ruby into 2.2
Add 2.2 Wheezy, also based on the 2.1 Dockerfile
Merge pull request #28 from misfo/2.2

Ruby 2.2 Dockerfiles