fix backend docker build

Author: karmaking

Dockerfiles/Dockerfile_backend

@@ -16,4 +16,4 @@ COPY --from=builder /home/node/app/dist-server /home/node/app
 RUN mkdir /home/node/node_modules
 COPY --from=builder /home/node/app/node_modules /home/node/node_modules
 WORKDIR /home/node/app
-CMD ["node", "app.js"]
+CMD ["node", "server/app.js"]