Escape cron step values with backslash (#2032)

* Escape cron step values with backslash

Escape cron step values with backslash in $CRON_MIN

* Change sed delimiter to allow unescaped slashes

Docker/entrypoint.sh

@@ -6,7 +6,7 @@ chown -R :www-data .
 chmod -R g+r . && chmod -R g+w ./data/
 
 if [ -n "$CRON_MIN" ]; then
-	sed -r -i "/FreshRSS/s/^[^ ]+ /$CRON_MIN /" /var/spool/cron/crontabs/root
+	sed -r -i "\#FreshRSS#s#^[^ ]+ #$CRON_MIN #" /var/spool/cron/crontabs/root
 fi
 
 exec "$@"