Update squid.rb

Added --disable-eui otherwise you get a bunch of
ERROR: ARP / MAC / EUI-* operations not supported on this operating system.

on OS X Server 10.8.3 and presumably others (reported for 10.6.8 here: http://squid-web-proxy-cache.1019090.n4.nabble.com/ERROR-ARP-MAC-EUI-operations-not-supported-on-this-operating-system-td4659335.html)