Experimenting with using Travis for a Racket project.

Travis doesn't have built-in support for Racket. However it seems this
should be do-able, anyway, by using `before_install` to install
Racket?

[![Build Status](https://travis-ci.org/[greghendershott]/[travis-racket].png)](https://travis-ci.org/[greghendershott]/[travis-racket])