Upgrade to traceur 0.0.72.

Compile and generate source maps with the new 0.0.72 API.
Added a test to confirm the creation of source maps.
here how you can correctly test source map support: https://github.com/sindresorhus/gulp-esnext/blob/5fd44c1dffbfe9f3aac1480db5caf8fdab0f7495/test.js#L27-L51