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.
`%p` was a typo. `%o` is a new feature in debug@2 for `util.inspect` format, which is sometimes easier on the eyes than `%j`'s JSON formatting.