changed to RSpec's expect syntax

I decided to change clearance to expect syntax for a project I was working on.  If, you want what I did, great!  If, not, you can just close this.

Please note, I have not done a poll request before.  If I have done it incorrectly, I apologize.
use the has format for the finder:
`user = Clearance.configuration.user_model.exists?(email: email)`