Update install GKE video in docs
The video we provide within our docs to demo installing GitLab on GKE needs updating to reflect our new changes to that flow.
doc/install/README.md
34:- [Install GitLab on Google Container Engine (GKE)](https://about.gitlab.com/2017/01/23/video-tutorial-idea-to-production-on-google-container-engine-gke/): video tutorial on
Current video: https://www.youtube.com/watch?v=3A8mdJl_icM