Use `longest` instead of `max`

This fixes [issues](https://github.com/google/web-starter-kit/issues/490#issuecomment-60008429) with npm due to a stupid deeply nested dependency (https://gist.github.com/sindresorhus/accb44d6eff6cbc24984#file-gistfile1-txt-L20). Also gets rid of that long dependency tree which shouldn't be needed for a log module.