Support SOCKS proxy from HTTP[S]_PROXY env vars

The recent release of [Requests 2.10.0][requests] with [this
update][urllib3-socks] to [urllib3][urllib3-release]
means that docker-compose can support a SOCKS proxy configured
via the HTTP[S]_PROXY environment variables.
We simply need to update the version of requests to
2.10.0, with the 'socks' extra, and the rest just works.

Signed-off-by: Brett Higgins <brhiggins@arbor.net>

[pysocks]: https://github.com/Anorov/PySocks
[requests]: https://github.com/kennethreitz/requests/pull/2953
[urllib3-socks]: urllib3/urllib3#762
[urllib3-release]: https://github.com/shazow/urllib3/blob/master/CHANGES.rst#114-2015-12-29

Signed-off-by: Brett Higgins <brhiggins@arbor.net>

requirements.txt

@@ -5,7 +5,7 @@ dockerpty==0.4.1
 docopt==0.6.1
 enum34==1.0.4
 jsonschema==2.5.1
-requests==2.7.0
+requests[socks]==2.10.0
 six==1.7.3
 texttable==0.8.4
 websocket-client==0.32.0

setup.py

@@ -31,7 +31,7 @@ def find_version(*file_paths):
     'cached-property >= 1.2.0, < 2',
     'docopt >= 0.6.1, < 0.7',
     'PyYAML >= 3.10, < 4',
-    'requests >= 2.6.1, < 2.8',
+    'requests[socks] >= 2.10.0',
     'texttable >= 0.8.1, < 0.9',
     'websocket-client >= 0.32.0, < 1.0',
     'docker-py >= 1.8.0, < 2',