Update setup.py with new docker-py minimum

Signed-off-by: Aanand Prasad <[email protected]>

setup.py

@@ -30,7 +30,7 @@ install_requires = [
     'requests >= 2.6.1, < 2.7',
     'texttable >= 0.8.1, < 0.9',
     'websocket-client >= 0.11.0, < 1.0',
-    'docker-py >= 1.2.2, < 1.3',
+    'docker-py >= 1.2.3-rc1, < 1.3',
     'dockerpty >= 0.3.4, < 0.4',
     'six >= 1.3.0, < 2',
 ]