gluon-autoupdater: fix incomplete comment in upgrade script

Fixes #1043

package/gluon-autoupdater/luasrc/lib/gluon/upgrade/500-autoupdater

@@ -41,7 +41,9 @@ autoupdater_util.randomseed()
 
 
 -- Perform updates at a random time between 04:00 and 05:00, and once an hour
+-- a fallback update (used after the regular updates haven't worked for
+-- (priority+1) days after a firmware release, for example because the node
+-- is always offline at night)
 local minute = math.random(0, 59)
 
 local f = io.open('/usr/lib/micron.d/autoupdater', 'w')