Clean up the oopsie. Rebuild the blank exercises.

node_modules/lodash/invertBy.js

@@ -7,6 +7,13 @@ var objectProto = Object.prototype;
 /** Used to check objects for own properties. */
 var hasOwnProperty = objectProto.hasOwnProperty;
 
+/**
+ * Used to resolve the
+ * [`toStringTag`](http://ecma-international.org/ecma-262/7.0/#sec-object.prototype.tostring)
+ * of values.
+ */
+var nativeObjectToString = objectProto.toString;
+
 /**
  * This method is like `_.invert` except that the inverted object is generated
  * from the results of running each element of `object` thru `iteratee`. The
@@ -34,6 +41,11 @@ var hasOwnProperty = objectProto.hasOwnProperty;
  * // => { 'group1': ['a', 'c'], 'group2': ['b'] }
  */
 var invertBy = createInverter(function(result, value, key) {
+  if (value != null &&
+      typeof value.toString != 'function') {
+    value = nativeObjectToString.call(value);
+  }
+
   if (hasOwnProperty.call(result, value)) {
     result[value].push(key);
   } else {