Docker cleanup. (#8226)

Dockerfile

@@ -1,3 +1,7 @@
+# Notice:
+# When updating this file, please also update virtualization/Docker/Dockerfile.dev
+# This way, the development image and the production image are kept in sync.
+
 FROM python:3.6
 MAINTAINER Paulus Schoutsen <Paulus@PaulusSchoutsen.nl>
 
@@ -21,6 +25,7 @@ RUN virtualization/Docker/setup_docker_prereqs
 
 # Install hass component dependencies
 COPY requirements_all.txt requirements_all.txt
+
 # Uninstall enum34 because some depenndecies install it but breaks Python 3.4+.
 # See PR #8103 for more info.
 RUN pip3 install --no-cache-dir -r requirements_all.txt && \