gluon-alfred: no parallel cronjobs

This should reduce memory consumption a little.

https://github.com/freifunk-gluon/gluon/issues/109#issuecomment-61681696

package/gluon-alfred/files/lib/gluon/cron/alfred

-* * * * * /lib/gluon/announce/announce.lua nodeinfo | gzip | alfred -s 158
-* * * * * /lib/gluon/announce/announce.lua statistics | gzip | alfred -s 159
+* * * * * /lib/gluon/announce/announce.lua nodeinfo | gzip | alfred -s 158; /lib/gluon/announce/announce.lua statistics | gzip | alfred -s 159