fix dockerfile

Dockerfile

@@ -16,6 +16,7 @@ RUN npm run build
 RUN DATABASE_URL=postgres://x/x \
     SECRET_KEY=x \
     ALLOWED_HOSTS=x \
+    CHOBOTNICE_RV_GID=x \
     python manage.py collectstatic --noinput --settings=rybicka.settings.prod
 
 RUN bash -c "adduser --disabled-login --quiet --gecos app app &&  \