Passing redirectPath a function is broken on oauth2

[yocontra]

https://github.com/bnoguchi/everyauth/blob/master/lib/modules/oauth2.js#L305-L310

Does not return this, so the chain is killed. I don't think this works either - this block is confusing and undocumented.

Expected behavior:

• Return this so you can keep chaining
• redirectPath function gets passed req and res arguments, and returns a string