[gps_ubx] fix months in date field

firmware/src/gps_ubx.c

@@ -446,7 +446,7 @@ struct gps_data_t gps_get_data(void)
   /* GPS Time */
   struct ubx_nav_timeutc timeutc = gps_get_nav_timeutc();
   data.year = timeutc.payload.year;
-  data.month = timeutc.payload.month;
+  data.month = timeutc.payload.month + 1; /* apparently needed */
   data.day = timeutc.payload.day;
   data.hour = timeutc.payload.hour;
   data.minute = timeutc.payload.min;