fix a lot of Tkinter imports
diff --git a/Demo/tkinter/guido/brownian.py b/Demo/tkinter/guido/brownian.py
index 8007f14..7ab3e67 100644
--- a/Demo/tkinter/guido/brownian.py
+++ b/Demo/tkinter/guido/brownian.py
@@ -1,6 +1,6 @@
 # Brownian motion -- an example of a multi-threaded Tkinter program.
 
-from Tkinter import *
+from tkinter import *
 import random
 import threading
 import time