www/linux-c6-flashplugin11: reintroduce gdkpixbuf2 dependency

• reintroduce gdkpixbuf2 dependency fixes regression introduced in r373192.
• bump PORTREVISION

Spotted by: zaphod@berentweb.com
Differential Revision: https://reviews.freebsd.org/D1268
Discussed on: emulation@
Approved by: koobs (mentor)