Fixed typo on Router Nat datasource docs (#15917)

Author: melinath

mmv1/third_party/terraform/website/docs/d/compute_router_nat.html.markdown

@@ -6,7 +6,7 @@ description: |-
 
 # google_compute_router_nat
 
-To get more information about Snapshot, see:
+To get more information about RouterNat, see:
 
 * [API documentation](https://cloud.google.com/compute/docs/reference/rest/v1/routers)
 * How-to Guides