fix bind in create_fake_connection

[slingamn]

Fixes this issue:

        if isinstance(source_address, tuple) and len(source_address) == 2:
>           source_address[1] = int(source_address[1])
E           TypeError: 'tuple' object does not support item assignment

I love this library! I'm working on switching a project from Requests to mureq. Except for this issue, all the existing httpretty mocking worked flawlessly, with no changes required.

[gabrielfalcao]

Hey @slingamn thank you so much for your contribution and please accept my sincere apologies for the delay.
Awesome PR, what a nice find!