Icedove package needs update, following IceCat 68.9.0 update.

[Mark H Weaver]

Hi,

I just pushed the IceCat-68.9.0 security update to the master branch of
Guix, along with a graft for NSS.

However, I just noticed that we now have Icedove in Guix, and that it's
based on 'icecat-source'.  This is all good and proper (kudos to all who
worked on it!), but unfortunately I didn't know about it until now, and
my IceCat update may have left Icedove in a bad state.  Can someone else
take care of updating Icedove?  I've run out of available time to work
on this at the moment.

     Thanks,
       Mark