change Dockerfile - npm install with production flag

Dockerfile

@@ -4,7 +4,7 @@ WORKDIR /peer-server
 COPY bin ./bin
 COPY dist ./dist
 COPY package.json .
-RUN npm install
+RUN npm install --production
 EXPOSE 9000
 ENTRYPOINT ["node", "bin/peerjs"]
 CMD [ "--port", "9000", "--path", "/myapp" ]