When creating a UDFTimestamp object, tm_month was copied into (#117)

both the month and the day field.
This resulted in bogus timestamps in the final iso.

pycdlib/udf.py

@@ -1115,7 +1115,7 @@ def new(self, date_seconds):
         self.timetype = 1
         self.year = local.tm_year
         self.month = local.tm_mon
-        self.day = local.tm_mon
+        self.day = local.tm_mday
         self.hour = local.tm_hour
         self.minute = local.tm_min
         self.second = local.tm_sec