Update dashboard version to v1.8.0

Update dependencies to be compatible with Kubernetes v1.8

roles/kubernetes-apps/ansible/defaults/main.yml

@@ -39,9 +39,9 @@ netchecker_server_cpu_requests: 50m
 netchecker_server_memory_requests: 64M
 
 # Dashboard
-dashboard_enabled: false
+dashboard_enabled: true
 dashboard_image_repo: gcr.io/google_containers/kubernetes-dashboard-amd64
-dashboard_image_tag: v1.7.1
+dashboard_image_tag: v1.8.0
 dashboard_init_image_repo: gcr.io/google_containers/kubernetes-dashboard-init-amd64
 dashboard_init_image_tag: v1.0.1