message: fix xds proto doc
diff: @@ -77,7 +77,7 @@ API flow
  For typical HTTP routing scenarios, the core resource types for the client's configuration are
  `Listener`, `RouteConfiguration`, `Cluster`, and `ClusterLoadAssignment`. Each `Listener` resource
  may point to a `RouteConfiguration` resource, which may point to one or more `Cluster` resources,
  -and each Cluster` resource may point to a `ClusterLoadAssignment` resource.
  +and each `Cluster` resource may point to a `ClusterLoadAssignment` resource.
  Envoy fetches all `Listener` and `Cluster` resources at startup. It then fetches whatever
  `RouteConfiguration` and `ClusterLoadAssignment` resources that are required by the `Listener` and
  