Revert "Removed Docker image build line that updates the CSS asset bu…

…ild filters."

This reverts commit 05e2f13.

docker/Dockerfile

@@ -38,7 +38,7 @@ COPY . /build
 # Prepare assets
 RUN yarn install --pure-lockfile --production && \
     yarn cache clean && \
-    #sed -i -r -e "s|'rcssmin',\s?'cssrewrite'|'rcssmin'|g" /build/powerdnsadmin/assets.py && \
+    sed -i -r -e "s|'rcssmin',\s?'cssrewrite'|'rcssmin'|g" /build/powerdnsadmin/assets.py && \
     flask assets build
 
 RUN mv /build/powerdnsadmin/static /tmp/static && \