www/squid3: Add official security patch SQUID-2018_3

Add security patch for SQUID-2018_3.

Bump PKGREVISION.

http://www.squid-cache.org/Advisories/SQUID-2018_3.txt

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Problem Description:

Due to incorrect pointer handling Squid is vulnerable to denial
of service attack when processing ESI responses.

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Severity:

This problem allows a remote server delivering ESI responses
to trigger a denial of service for all clients accessing the
Squid service.

This problem is limited to Squid operating as reverse proxy.

(taca)