Tweak example to handle changes to Python 3.6's integer formatting.

Fixes #167.

pep-0498.txt

@@ -116,7 +116,7 @@ and ``datetime``). This example is not possible with
 ``string.Template``::
 
   >>> value = 1234
-  >>> f'input={value:#0.6x}'
+  >>> f'input={value:#06x}'
   'input=0x04d2'
 
 And neither %-formatting nor ``string.Template`` can control