/etc/logrotate.d/squid3 is in squid3 3.3.8-1ubuntu6.11.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18  | #
#	Logrotate fragment for squid3.
#
/var/log/squid3/*.log {
	daily
	compress
	delaycompress
	rotate 2
	missingok
	nocreate
	sharedscripts
	prerotate
		test ! -x /usr/sbin/sarg-reports || /usr/sbin/sarg-reports
	endscript
	postrotate
		test ! -e /var/run/squid3.pid || test ! -x /usr/sbin/squid3 || /usr/sbin/squid3 -k rotate
	endscript
}
 |