Disallow event global variable with no-restricted-globals rule (facebook#1530) (facebook#1532)

* Disallow event global variable with no-restricted-globals rule (facebook#1530)

* changed event global variable usage liniting from warn to error

Author: vfil

Diff for: packages/eslint-config-react-app/index.js

@@ -123,6 +123,7 @@ module.exports = {
     'no-this-before-super': 'warn',
     'no-throw-literal': 'warn',
     'no-undef': 'error',
+    'no-restricted-globals': ['error', 'event'],
     'no-unexpected-multiline': 'warn',
     'no-unreachable': 'warn',
     'no-unused-expressions': ['warn', {