Add matching braces to prevent partial execution hazards

Instigated from this blog post lamenting the practice of running
programs directly from a pipe:

  http://blog.existentialize.com/dont-pipe-to-your-shell.html

This commit comes out with greater lucidity if one uses:

  $ git diff --ignore-all-space

Also throw in a shebang.
Specify Ruby version as per buildpack suggestion.