Resolve the model path before requiring models

[jacobwgillespie]

If your model path is ./models in options.models, then path.join will strip the leading ., leading to errors when the require is no longer relative (like Error: Cannot find module 'models/user.js').

This PR fixes this by calling path.resolve before calling require to turn relative paths into absolute ones.

Here's a related link: http://stackoverflow.com/questions/23096963/node-js-path-join-removes-leading-period

[coveralls]

Coverage remained the same at 100.0% when pulling 4d148b3 on playlist-forks:fix-relative-require into 7c4814d on lob:master.

[jacobwgillespie]

Thanks! 👍

[pon]

Thank you!