Post-release version bump to 1.8.1
Post-release version bump to 1.8.1

gcampax/cogl,Distrotech/cogl,gcampax/cogl,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl,djdeath/cogl,collects/cogl,Distrotech/cogl,gcampax/cogl,djdeath/cogl-android,collects/cogl,djdeath/cogl,djdeath/cogl,Distrotech/cogl,djdeath/cogl-android