Fix 'edgerouter x' sysupgrade link

[csensitive]

Hi,

Can you fix the link to the sysupgrade tar file in the edgerouter x.

http://downloads.openwrt.org/releases/19.07.0/targets/ramips/mt7621/openwrt-19.07.0-ramips-mt7621-ubnt-erx-squashfs-sysupgrade.tar

It returns a 404 not found.

Thanks in advance.

[tmomas]

Related: Edgerouter X wiki points to not working .BIN and other thingies

Someone should clarify why there is only a .bin while a .tar seems to be needed.