www/palemoon: Update to 27.7.2

• Attempt to fix build with Clang 6 [1]

Changes: http://www.palemoon.org/releasenotes.shtml
PR: 225644, 225280 [1]
Approved by: lichray@gmail.com (maintainer)
Security: 5044bd23-08cb-11e8-b08f-00012e582166