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.
I'd get rid of the previous line and inline it like so:

`expect(headers).to set_cookie(
  'remember_token',
  user.remember_token,
  remembered_expires
)
```

The expectation you have hear doesn't read very well.