Reorder Key Vault code owners (Azure#24704)

Some tools seem to use the first person as the de facto owner.

Author: heaths

.github/CODEOWNERS

@@ -343,7 +343,7 @@
 /sdk/iothub/Microsoft.Azure.Management.IotHub/            @rkmanda @chieftn
 
 # PRLabel: %KeyVault
-/sdk/keyvault/                                  @schaabs @heaths
+/sdk/keyvault/                                  @heaths @schaabs
 
 # ServiceLabel: %Kubernetes Configuration %Service Attention
 /sdk/kubernetesconfiguration/Microsoft.Azure.Management.KubernetesConfiguration/            @NarayanThiru