Fix versions of grafana and grafana-bootstrap

Stick to stable versions for now, seems to fix issues with metrics not appearing.

docker/docker-compose.yml

@@ -8,7 +8,7 @@ services:
       volumes:
             - ./sitespeed-result/:/sitespeed.io/sitespeed-result
     grafana:
-      image: grafana/grafana:4.1.0-beta1
+      image: grafana/grafana:4.0.2
       depends_on:
         - graphite
       links:
@@ -33,7 +33,7 @@ services:
       volumes:
         - graphite:/opt/graphite/storage/whisper
     grafana-setup:
-      image: sitespeedio/grafana-bootstrap
+      image: sitespeedio/grafana-bootstrap:grafana-4.0
       links:
         - grafana
       environment: