fix legacy tests to work with requests>=2.12.4 (#82)

It seems that the internals of the requests library changed a few
times and broke different things after requests==2.11.1 which is
the version when the tests passed last. Then versions of requests
2.12.0, 2.12.1, 2.12.2, 2.12.3 all broke the tests and finally
version 2.12.4 worked but for the tests to pass we need the changes
from this commit.