fixed Node.rename (GitHub issue #6)

@@ -1865,6 +1865,9 @@ class Node (NetElement) :
         @param name: the new name of the node
         @param name: the new name of the node
         @type name: `str`
         @type name: `str`
         """
         """
+        try :
+            self.net.rename_node(self.name, name)
+        except AttributeError :
             self.name = name
             self.name = name
 
 
 class Place (Node) :
 class Place (Node) :