Fix internal linting setup and add missing headers (facebook#1741)

Author: gaearon

packages/react-scripts/config/jest/babelTransform.js

@@ -8,6 +8,8 @@
  */
 'use strict';
 
+'use strict';
+
 const babelJest = require('babel-jest');
 
 module.exports = babelJest.createTransformer({

packages/react-scripts/scripts/test.js

@@ -10,6 +10,8 @@
 // @remove-on-eject-end
 'use strict';
 
+'use strict';
+
 process.env.NODE_ENV = 'test';
 process.env.PUBLIC_URL = '';