[deps] Upgrade python-six to Debian 10 version as minimum

cubicweb_slickgrid/__pkginfo__.py

@@ -22,7 +22,7 @@ web = 'https://www.cubicweb.org/project/%s' % distname
 
 __depends__ = {
     'cubicweb': '>= 3.26.19',
-    'six': '>= 1.4.0',
+    'six': '>= 1.12.0',
 }
 __recommends__ = {}