fix: update root endpoint, fixes #1226, #1240

Author: theKashey

root.js

@@ -2,19 +2,24 @@ if (module.hot) {
   var hot = require('./index').hot;
   var cache = require.cache;
 
-  if (!module.parents || !module.parents[0]) {
+  if (!module.parents || module.parents.length === 0) {
     throw new Error(
       'React-Hot-Loader: `react-hot-loader/root` is not supported on your system. ' +
         'Please use `import {hot} from "react-hot-loader"` instead',
     );
   }
   // access parent
   var parent = cache[module.parents[0]];
-  // remove itself from a cache
+  if (!parent) {
+    throw new Error(
+      'React-Hot-Loader: `react-hot-loader/root` is not supported on your system. ' +
+        'Please use `import {hot} from "react-hot-loader"` instead',
+    );
+  }
+  // remove self from a cache
   delete cache[module.id];
   // setup hot for caller
-
-  exports.hot = hot(Object.assign({ id: parent.i }, parent));
+  exports.hot = hot(parent);
 } else {
   // prod mode
   exports.hot = function(a) {