chore(deps): update longhornio/longhorn-engine docker tag to v1.8.1

kubernetes/longhorn/helm/values.yaml

@@ -3,7 +3,7 @@ image:
   longhorn:
     engine:
       repository: "longhornio/longhorn-engine"
-      tag: "v1.8.0"
+      tag: "v1.8.1"
     manager:
       repository: "longhornio/longhorn-manager"
       tag: "v1.8.1"