Fix npm2 support

Problem: `npm run build` fails on npm2 if there is no `build` run-script defined.
Fix: Only run `npm run build` step if there is a `build` run-script defined.

The fix is easy, but I'm going to spend a few minutes trying to get CI green if I can.
`%o` and `%p` are not documented console.log flags. http://nodejs.org/api/util.html#util_util_format_format  What are they from?