update docker-py requirement to use master branch

Signed-off-by: Jonathan Stewmon <[email protected]>

requirements.txt

@@ -1,8 +1,8 @@
 PyYAML==3.11
-docker-py==1.6.0
 dockerpty==0.3.4
 docopt==0.6.1
 enum34==1.0.4
+git+https://github.com/docker/docker-py.git@master#egg=docker-py
 jsonschema==2.5.1
 requests==2.7.0
 six==1.7.3