Remove therubyracer dependency

* We don't need it in production on Heroku, and installing node is a
  reasonable alternative in development.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Bump debugger to a Ruby 2.0.0-compatible version

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Add basic Travis CI configuration

Signed-off-by: Alex Coles <alex@alexbcoles.com>