Uninstall enum34 in python3.6 docker image (home-assistant#8103)

* Uninstall enum34 in python3.6 docker image

This is a short term fix for home-assistant#7733

What's happening is the following dependencies are pulling enum34:
- pygatt
- libsoundtouch
- yeelight
However, enum34 is not meant to be installed in Python versions 3.4+
and causing the `AttributeError: module 'enum' has no attribute 'IntFlag'``

I've submitted patches to these projects so we don't have to do this
manual uninstall in the future.

* Update Dockerfile

Dockerfile

@@ -21,8 +21,11 @@ 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 && \
-    pip3 install --no-cache-dir mysqlclient psycopg2 uvloop cchardet
+    pip3 install --no-cache-dir mysqlclient psycopg2 uvloop cchardet && \
+    pip3 uninstall enum34
 
 # Copy source
 COPY . .