Support py2 and py3

Author: bmoscon

arctic/date/_mktz.py

@@ -33,7 +33,7 @@ def mktz(zone=None):
     """
     if zone is None:
         zone = tzlocal.get_localzone().zone
-    zone = six.u(zone, 'ascii')
+    zone = six.u(zone)
     tz = dateutil.tz.gettz(zone)
     if not tz:
         raise TimezoneError('Timezone "%s" can not be read' % (zone))