bump docker-py

Signed-off-by: Jessica Frazelle <acidburn@docker.com>

Dockerfile

@@ -163,7 +163,7 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Get the "docker-py" source so we can run their integration tests
-ENV DOCKER_PY_COMMIT 47ab89ec2bd3bddf1221b856ffbaff333edeabb4
+ENV DOCKER_PY_COMMIT 57512760c83fbe41302891aa51e34a86f4db74de
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \
 	&& git checkout -q $DOCKER_PY_COMMIT \