Added upper version boundry for six

The 1.4.0 version of six is not compatible with WSME 0.5b2.

This fixed bug #1219694.

Change-Id: Ifecf321865c98990b049d5df5de23eb1c90fd6c4
(cherry picked from commit 4e3351bc250a0b6278d71c4e6b88a147a9c762f5)