Run in child process instead of lazy loading every dependency

Not a big fan [of lazy loading], but I've seen update-notifier as a require time offender when profiling various things. The idea of update-notifier is that it should have no impact on the consumer. It's just an added bonus, not critical. https://github.com/yeoman/update-notifier/pull/82#issuecomment-225636213

I may be wrong, it seems to me that this change was made simply to hide the package from the very initial load but in practice every dependency is still loaded right after.

update-notifier already uses a child process to do the checking, so I think it'd be best to do the whole thing there.

Related:

• https://github.com/yeoman/update-notifier/issues/80
• https://github.com/yeoman/update-notifier/pull/82