Offer to set default browsers (#3792)

* Offer to set browser defaults

* Catch error on no

* Add ending newlines

* Ensure we re-check to prevent defaults from leaking

* Reduce nesting

* Add defaults message

* More explicit

packages/react-scripts/scripts/eject.js

@@ -22,6 +22,7 @@ const paths = require('../config/paths');
 const createJestConfig = require('./utils/createJestConfig');
 const inquirer = require('react-dev-utils/inquirer');
 const spawnSync = require('react-dev-utils/crossSpawn').sync;
+const os = require('os');
 
 const green = chalk.green;
 const cyan = chalk.cyan;
@@ -218,7 +219,7 @@ inquirer
 
     fs.writeFileSync(
       path.join(appPath, 'package.json'),
-      JSON.stringify(appPackage, null, 2) + '\n'
+      JSON.stringify(appPackage, null, 2) + os.EOL
     );
     console.log();