fix(documentarray): use toObject() instead of cloning for inspect

Re: #6637

Author: vkarpov15

lib/types/documentarray.js

@@ -265,7 +265,7 @@ MongooseDocumentArray.mixin = {
    */
 
   inspect: function() {
-    return Array.prototype.slice.call(this);
+    return this.toObject();
   },
 
   /**