Fix for getting of monday for a given week.

bin/timelapse_weekly.sh

@@ -14,7 +14,7 @@ else
 fi
 current_week=`date +'%V'`
 current_week_diff=$((${current_week}-${WEEK}))
-DATE_WEEK=`date --date="${current_week_diff} weeks ago" +%Y%m%d`
+DATE_WEEK=`date --date="last monday - ${current_week_diff} weeks" +%Y%m%d`
 DATE_START=`date --date="${DATE_WEEK}" +%s`
 DATE_STOP=$(($DATE_START+7*86400))