Use pause image from new source.

Signed-off-by: Lantao Liu <lantaol@google.com>

docs/config.md

@@ -16,7 +16,7 @@ The explanation and default value of each configuration item are as follows:
   enable_selinux = false
 
   # sandbox_image is the image used by sandbox container.
-  sandbox_image = "gcr.io/google_containers/pause:3.1"
+  sandbox_image = "k8s.gcr.io/pause:3.1"
 
   # stats_collect_period is the period (in seconds) of snapshots stats collection.
   stats_collect_period = 10

docs/crictl.md

@@ -185,7 +185,7 @@ $ crictl info
       }
     },
     "streamServerPort": "10010",
-    "sandboxImage": "gcr.io/google_containers/pause:3.0",
+    "sandboxImage": "k8s.gcr.io/pause:3.1",
     "statsCollectPeriod": 10,
     "containerdRootDir": "/var/lib/containerd",
     "containerdEndpoint": "/run/containerd/containerd.sock",