Update keyvault.json (Azure#11040)

* Update keyvault.json

* Update keyvault.json

* Update keyvault.json

Author: jlichwa

specification/keyvault/resource-manager/Microsoft.KeyVault/stable/2019-09-01/keyvault.json

@@ -1112,7 +1112,7 @@
         },
         "vaultUri": {
           "type": "string",
-          "description": "The URI of the vault for performing operations on keys and secrets."
+          "description": "The URI of the vault for performing operations on keys and secrets. This property is readonly"
         },
         "enabledForDeployment": {
           "type": "boolean",