Use local websockify when building container

It's very surprising to get some external copy of websockify when you
are building an image in your local websockify source tree. Make sure we
are using the local copy of everything.

docker/Dockerfile

@@ -1,12 +1,9 @@
-FROM python:3.6
+FROM python
 
-ENV VERSION 0.10.0
+COPY websockify-*.tar.gz /
 
-RUN mkdir -p /opt/websockify \
-    && curl -SL https://github.com/novnc/websockify/archive/refs/tags/v$VERSION.tar.gz \
-    | tar xzC /opt/websockify
-
-RUN python -m pip install 'numpy<1.17' redis simplejson jwcrypto requests
+RUN python3 -m pip install websockify-*.tar.gz
+RUN rm -rf /websockify-* /root/.cache
 
 VOLUME /data
 
@@ -15,7 +12,5 @@ EXPOSE 443
 
 WORKDIR /opt/websockify
 
-COPY docker-entrypoint.sh /
-
-ENTRYPOINT ["/docker-entrypoint.sh"]
+ENTRYPOINT ["/usr/local/bin/websockify"]
 CMD ["--help"]