Drop --no-cache as well

Since several of our services share the same image, this should speed up
building a good bit, and --no-cache shouldn't be necessary - if we're
still having issues with things not updating, we should figure out how
to arrange the Dockerfile, but I think it should be fine as-is.

bw-dev

@@ -80,7 +80,7 @@ case "$CMD" in
         ;;
     update)
         git pull
-        docker-compose build --no-cache
+        docker-compose build
         runweb python manage.py migrate
         runweb python manage.py collectstatic --no-input
         docker-compose up -d