docs: fix typo in GCP network_peering.network_name (#498)

The "GCP ONLY" section of the `network_peering` has a wrong reference to AWS.

Author: daquinoaldo

website/docs/r/network_peering.html.markdown

@@ -332,7 +332,7 @@ resource "mongodbatlas_network_peering" "test" {
 **GCP ONLY:**
 
 * `gcp_project_id` - (Required - GCP) GCP project ID of the owner of the network peer.
-* `network_name` - (Required- AWS) Name of the network peer to which Atlas connects.
+* `network_name` - (Required - GCP) Name of the network peer to which Atlas connects.
 
 **AZURE ONLY:**