Upgrade to docker-py 3.2.1

clean_registry.py

@@ -197,6 +197,8 @@ class RegistryCleaner():
 
         if self.container is not None:
             self.docker.api.start(self.container)
+            self.docker.close()
+
         return exit_status
 
     def get_file(self, path):

requirements.txt

@@ -2,7 +2,7 @@ backports.ssl-match-hostname==3.5.0.1
 backports.weakref==1.0.post1
 certifi==2018.1.18
 chardet==3.0.4
-docker==3.1.0
+docker==3.2.1
 docker-pycreds==0.2.2
 idna==2.6
 pkg-resources==0.0.0