Update index.js (facebook#1603)

To avoid file conflict issue with IJ static web projects

Author: driquelme

packages/create-react-app/index.js

@@ -311,7 +311,7 @@ function moveReactScriptsToDev(packageName) {
 // https://github.com/facebookincubator/create-react-app/pull/368#issuecomment-243446094
 function isSafeToCreateProjectIn(root) {
   var validFiles = [
-    '.DS_Store', 'Thumbs.db', '.git', '.gitignore', '.idea', 'README.md', 'LICENSE'
+    '.DS_Store', 'Thumbs.db', '.git', '.gitignore', '.idea', 'README.md', 'LICENSE', 'web.iml'
   ];
   return fs.readdirSync(root)
     .every(function(file) {