Reduce amount of checked mirrors

configs/releng/airootfs/etc/xdg/reflector/reflector.conf:
Reduce the amount mirrors that reflector checks from 70 to 20.
This significantly reduces the time it takes to end up with an up-to-date mirrorlist during boot with the releng
profile.

Fixes #92

configs/releng/airootfs/etc/xdg/reflector/reflector.conf

@@ -2,5 +2,5 @@
 
 --save /etc/pacman.d/mirrorlist
 --protocol https
---latest 70
+--latest 20
 --sort rate