docs(schema): add missing jsdoc to DocumentArrayElement.prototype.clone re: #13190

Author: vkarpov15

lib/schema/DocumentArrayElement.js

@@ -75,6 +75,13 @@ DocumentArrayElement.prototype.doValidate = function(value, fn, scope, options)
   return SubdocumentPath.prototype.doValidate.call(this, value, fn, scope, options);
 };
 
+/**
+ * Clone the current SchemaType
+ *
+ * @return {DocumentArrayElement} The cloned instance
+ * @api private
+ */
+
 DocumentArrayElement.prototype.clone = function() {
   this.options.$parentSchemaType = this.$parentSchemaType;
   const ret = SchemaType.prototype.clone.apply(this, arguments);