fix: parse object proto pollution

Author: Moumouls

src/ParseObject.ts

@@ -102,7 +102,7 @@ type ToJSON<T> = {
 
 // Mapping of class names to constructors, so we can populate objects from the
 // server with appropriate subclasses of ParseObject
-const classMap: AttributeMap = {};
+const classMap: AttributeMap = Object.create(null);
 
 // Global counter for generating unique Ids for non-single-instance objects
 let objectCount = 0;