Use correct class name when creating instance of lazy loading dict...

opcua/server/address_space.py

@@ -504,7 +504,7 @@ class AddressSpace(object):
             def __len__(self):
                 raise NotImplementedError
 
-        self._nodes = LazyLoader(shelve.open(path, "r"))
+        self._nodes = LazyLoadingDict(shelve.open(path, "r"))
 
     def get_attribute_value(self, nodeid, attr):
         with self._lock: