Fix Python typo.

python.html.markdown

@@ -191,7 +191,7 @@ li[2:]  # => [4, 3]
 li[:3]  # => [1, 2, 4]
 # Select every second entry
 li[::2]   # =>[1, 4]
-# Revert the list
+# Reverse the list
 li[::-1]   # => [3, 4, 2, 1]
 # Use any combination of these to make advanced slices
 # li[start:end:step]