message: use one less core for server
diff: @@ -9,7 +9,8 @@ function resolve(file) {
  return path.resolve(__dirname, file);
  }
  -const numCPUs = require('os').cpus().length;
  +// Leave one free worker so we have a core for old prerender service.
  +const numWorkers = require('os').cpus().length - 1;
  const isProd = process.env.NODE_ENV === 'production';
  const section = argv.section || 'app';
  const serverBuildPath = isProd ? '../../build/prod-server/' : '../build/dev-server/';
  @@ -28,7 +29,7 @@ if (cluster.isMaster) {
  console.log(`Master ${process.pid} is running`);
  // Fork workers.
  - for (let i = 0; i < numCPUs; i++) {
  + for (let i = 0; i < numWorkers; i++) {
  cluster.fork();
  }
  