Does not work on OSX Darwin

[brunson]

The use of TCPKeepAliveAdapter from requests-toolbelt means that the marathon client doesn't work on Mac OS X. It is fixed in the upstream in the commit below, but is not release by the requests team.

requests/toolbelt@ec4fb7c

This is just an informational notice to other users. Until requests releases the above fix, marathon-python doesn't work on Darwin without providing a self constructed connection to marathon SSE.