Use latest esp docker image with tag 1 (GoogleCloudPlatform#2358)

Author: qiwzhang

endpoints/kubernetes/grpc-bookstore.yaml

@@ -44,7 +44,7 @@ spec:
     spec:
       containers:
       - name: esp
-        image: gcr.io/endpoints-release/endpoints-runtime:1.16.0
+        image: gcr.io/endpoints-release/endpoints-runtime:1
         args: [
           "--http2_port=9000",
           "--service=SERVICE_NAME",