fix(document): copy date objects correctly when strict = false

Fix #7907

Author: vkarpov15

lib/document.js

@@ -844,7 +844,7 @@ Document.prototype.$set = function $set(path, val, type, options) {
     }
 
     if (typeof path[key] === 'object' &&
-        !Array.isArray(path[key]) &&
+        !utils.isNativeObject(path[key]) &&
         path[key] != null &&
         pathtype !== 'virtual' &&
         pathtype !== 'real' &&

lib/utils.js

@@ -494,6 +494,19 @@ exports.isPOJO = function isPOJO(arg) {
   return !proto || proto.constructor.name === 'Object';
 };
 
+/*!
+ * Determines if `obj` is a built-in object like an array, date, boolean,
+ * etc.
+ */
+
+exports.isNativeObject = function(arg) {
+  return Array.isArray(arg) ||
+    arg instanceof Date ||
+    arg instanceof Boolean ||
+    arg instanceof Number ||
+    arg instanceof String;
+};
+
 /*!
  * Search if `obj` or any POJOs nested underneath `obj` has a property named
  * `key`