Update oauth2.py

[grigoriysol]

Теперь версия '&v=5.103' в запросах к api VK - обязательный параметр: https://vk.com/dev/api_requests

[mrichar1]

Thanks for spotting this new requirement.

We could accept this patch if the version was configurable. If you look at the foursquare oauth2 provider, it also has a v param - see the code here:

https://github.com/authomatic/authomatic/blob/master/authomatic/providers/oauth2.py#L1069

If you can change your PR to work in the same way, and also add docs (via the docstrings - see FourSquare's) we can look at merging this in. Thanks!