Fix error when Instagram return lowercase "content-location"

[zztalker]

Catch a strange error - instagram return in headers lowercased "content-location".

[zztalker]

There is the error in design because of the response of request module already lowercase headers. And enough to make one check ('content-location' in response).

[wkoot]

Why not response.get('content-location', response['Content-Location']) ?

Anyway - the Instagram v1 API this library uses, has been deprecated and will be discontinued.
A lot of instagram endpoints are already no longer available: https://www.instagram.com/developer/changelog/

[zztalker]

Because response['Content-Location'] rise KeyError exception.
But it's still working, and why not to fix some errors - and publish it on PyPI warehouse?

[wkoot]

The point is that it should not fail silently; either 'Content-Location' or 'content-location' should be tried.
If neither of these headers are there, raising an exception is correct. Might be nicer to raise a OAuth2AuthExchangeError ofc