Increase version number

--HG--
branch : 6.0

tryton/__init__.py

@@ -1,6 +1,6 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
-__version__ = "6.0.20"
+__version__ = "6.0.21"
 import gi
 import locale