Don’t import typing.Deque at runtime (for Python < 3.5.4)
Don’t import typing.Deque at runtime (for Python < 3.5.4)

On Ubuntu 16.04, which has Python 3.5.2, `apns2.client` failed to
import, because `typing.Deque` was not added until Python 3.5.4.

Fixes #88.

Signed-off-by: Anders Kaseorg <087231934ba8fcf78bc142ce37d193b895ac03c4@mit.edu>

Pr0Ger/PyAPNs2