Hotfix for #3289 `ReflectionParameter#getClass()` on `callable` type hint should not raise exceptions

See #3289 - `ReflectionParameter#getClass()` on `callable` type hint should not raise exceptions

PR is NOT tested as I didn't have time to build HHVM today, so I'll have to trust travis here.
@bauerj given that this diff was already "ruined" by a missing trailing comma, I'd say that it makes a lot of sense to have a trailing comma now ;-)