Detect HTTPS links in content_type()

[guludo]

Hi there,

This allows downloading files provided via https links.

This PR fixes #258 .

Best regards,
Gustavo Sousa

[benureau]

It's a simple but critical improvement. I would prefer having a test for this, but I am not sure that downloading a file of the internet with unit test is a good idea. I will look into it.

[omangin]

I would prefer having a test for this, but I am not sure that downloading a file of the internet with unit test is a good idea.

Let's add first a simple unit test for the content_type method that the PR changes. Then is should be feasible to just mock the urlopen imported in the module to get a functional test that does not rely on an internet connection.

[benureau]

@guludo: I am merging this (sorry for the delay!). I will add a test for it, but I am decoupling that from merging this. See #271.

[guludo]

No worries! And thanks for applying. Sorry I couldn't help writing tests for it.