Dont use match on routes as wont work on rails4

### Problem
route `match` is not a thing anymore on rails 4+ .

### Solution
This replaces the syntax using a `delete`, however we cannot use `as: 'sign_out'` as on rails 4 you cannot override a route `as` value if that was defined before, which is the case in https://github.com/thoughtbot/clearance/blob/master/config/routes.rb#L20 . So we give it another key, but we as the path(`/sign_out`) is the same as the original, we can still use `sign_out_path` which will generate `/sign_out` and will pass through out custom route.

This is necessary for rails 4, and works on rails 3.2

r. @dwradcliffe @qrush
cc @georgedrummond