www/rubygem-rest-client: import two security fixes

This is a direct commit to branches/2015Q2, as rubygem-rest-client was
already updated to 1.8.0 in head.

PR: 200504
Differential Revision: https://reviews.freebsd.org/D2707
Approved by: ports-secteam (delphij)
Security: CVE-2015-1820
Security: CVE-2015-3448