fedora-cloud ruby Dockerfile

Try out a simple build:

$ sudo docker build -t <username>/ruby .
..
..
Complete!
Cleaning repos: fedora updates
Cleaning up everything
 ---> 5fbcdaa353c5
Removing intermediate container cda594a8b622
Successfully built 5fbcdaa353c5

Now launch an interactive ruby shell:

$ sudo docker run -it <username>/ruby irb
irb(main):001:0> 2 + 3
=> 5