fix docker package name
docker-py is the old package name
@@ -2,4 +2,4 @@ FROM python:3.6-alpine3.6
ADD image-cleaner.py /usr/local/bin/image-cleaner.py
-RUN pip3 install --no-cache-dir docker-py
\ No newline at end of file
+RUN pip3 install --no-cache-dir docker
