fixed bug in assignment operator

stdlib/mem.krak

@@ -181,6 +181,13 @@ obj shared_ptr<T> (Object){
     return *this; 
   }
   
+  fun operator=(newPtr: ref *T): ref shared_ptr<T> {
+      data = newPtr;
+      refCount = 1;
+      delete(newPtr,1);
+    return *this; 
+  }
+
 }; //end shared_ptr class