fix Dockerfile

packages/slackbot-proxy/docker/Dockerfile

@@ -37,7 +37,7 @@ RUN tar cf node_modules.tar node_modules \
 FROM deps-resolver-base AS deps-resolver-prod
 RUN npx lerna bootstrap -- --production
 # make artifacts
-RUN tar cf dependencies.tar
+RUN tar cf dependencies.tar \
   node_modules \
   packages/slack/node_modules \
   packages/slackbot-proxy/node_modules