fixes: local variable 'response' referenced before assignment

[lwille]

response won't be initialized in case an exception was thrown, causing the following error:

  File "/usr/local/lib/python2.7/site-packages/marathon/client.py", line 125, in _do_sse_request
    if response.ok:
UnboundLocalError: local variable 'response' referenced before assignment

[solarkennedy]

Looks fine. Can you address the pep8 thing?

./marathon/client.py:129:9: E303 too many blank lines (2)

[solarkennedy]

Month bump, can you address the flake errors? (optionally rebase on master)

[lwille]

closing outdated PR