doc and image update for release 1.4.9

Author: lizhuqi

README.md

@@ -12,7 +12,7 @@ lifecycle of Google Compute Engine Persistent Disks.
 ## Project Status
 
 Status: GA
-Latest stable image: `k8s.gcr.io/cloud-provider-gcp/gcp-compute-persistent-disk-csi-driver:v1.3.4`
+Latest stable image: `k8s.gcr.io/cloud-provider-gcp/gcp-compute-persistent-disk-csi-driver:v1.4.0`
 
 ### Test Status
 

deploy/kubernetes/images/stable-master/image.yaml

@@ -52,5 +52,5 @@ imageTag:
   # Don't change stable image without changing pdImagePlaceholder in
   # test/k8s-integration/main.go
   newName: k8s.gcr.io/cloud-provider-gcp/gcp-compute-persistent-disk-csi-driver
-  newTag: "v1.3.4"
+  newTag: "v1.4.0"
 ---