CI should check that example app always compiles

[divmain]

Alternately, write integration tests that take input of:

• interlock config
• input directory

And output

• bundles (without writing to disk)

Then assertions can be made about those bundles, similarly to how Babel tests are written.

[divmain]

Closing in favor of https://github.com/interlockjs/interlock/issues/47#issuecomment-212256859.