Prepare release 6.4.0 [skip ci]

CHANGELOG

@@ -1,3 +1,5 @@
+Version 6.4.0 - 2022-05-02
+* Bug fixes (see mercurial logs for details)
 * Add notification service option
 * Add support for Python 3.10
 * Remove support for Python 3.6

COPYRIGHT

@@ -1,5 +1,5 @@
-Copyright (C) 2016-2021 B2CK.
-Copyright (C) 2016-2017 Nicolas Évrard.
+Copyright (C) 2016-2022 B2CK.
+Copyright (C) 2016-2022 Nicolas Évrard.
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by

tryton.cfg

@@ -1,5 +1,5 @@
 [tryton]
-version=6.3.0
+version=6.4.0
 depends:
     ir
     res