resolve race condition when creating rd.json

scripts/build.js

@@ -13,14 +13,9 @@ process.on('unhandledRejection', err => {
     throw err;
 });
 
-// create radar
-
-require('../bin/tasks/radarjson').radarJsonGenerator()
-
 // Ensure environment variables are read.
 require('../config/env');
 
-
 const path = require('path');
 const chalk = require('react-dev-utils/chalk');
 const fs = require('fs-extra');
@@ -55,7 +50,8 @@ const config = configFactory('production');
 // We require that you explicitly set browsers and do not fall back to
 // browserslist defaults.
 const {checkBrowsers} = require('react-dev-utils/browsersHelper');
-checkBrowsers(paths.appPath, isInteractive)
+require('../bin/tasks/radarjson').radarJsonGenerator()
+    .then(checkBrowsers(paths.appPath, isInteractive))
     .then(() => {
         // First, read the current file sizes in build directory.
         // This lets us display how much they changed later.
@@ -134,6 +130,7 @@ checkBrowsers(paths.appPath, isInteractive)
         process.exit(1);
     });
 
+
 // Create the production build and print the deployment instructions.
 function build(previousFileSizes) {
     // We used to support resolving modules according to `NODE_PATH`.
@@ -215,3 +212,4 @@ function copyPublicFolder() {
         filter: file => file !== paths.appHtml,
     });
 }
+