Fix sessions not being saved after some exceptions

When handling, for instance, TokenMismatchException, the session was not being saved. Implementation follows Taylor comment in #laravel-dev:

    23:56:36 < TaylorOtwell> AntonioRibeiro: yeah i think session write middleware might just need a terminate implementation

You can get rid of the `$session = ` and the call to `with()` here. This should not have been merged yet