removed delete of the index.js

setup.js

@@ -17,7 +17,6 @@ writeFile('package.json', JSON.stringify(packageJson, null, 2));
 
 execSync(`npm i ${devDependencies.join(' ')} --save-dev --save-exact`);
 
-deleteFile('index.js');
 deleteFile('App.js');
 deleteFile('__tests__/App.js');
 deleteFile('.flowconfig');