Fix number of worker in development

src/server.js

@@ -14,7 +14,7 @@ if (!compatVersion()) {
 if(cluster.isMaster) {
     log.info(`Master ${process.pid} is running`);
 
-    const numCPUs = require('os').cpus().length;
+    const numCPUs = (process.env.NODE_ENV != 'development') ? require('os').cpus().length : 1;
     log.info(`Master will create ${numCPUs} workers`);
     for(let i=0; i < numCPUs; ++i) {
         cluster.fork();