New social providers and requests bug fix

Added linkedin and github providers.

Bumped requests to the newest version and made codebase compatible. This should fix the live tests.

@rdegges @omgitstom Please see the commit msg in this commit https://github.com/denibertovic/stormpath-sdk-python/commit/9dd5d66f2b9a31032da76bfbdee00c44aa74cc71

This change might break user code if they use requests in their codebase because the version of request (that contains the fixes we need) contains API breaking changes. But I don't see any way around this....