Update docs/node/nodes/gateway.md

Co-authored-by: Steffen Vogel <steffen.vogel@opal-rt.com>
Signed-off-by: al3xa23 <140614263+al3xa23@users.noreply.github.com>

Author: al3xa23

docs/node/nodes/gateway.md

@@ -98,7 +98,7 @@ message msg {
 
 ```
 
-### Call GetData method on gRPC server
+### Call `GetData` method on gRPC server
 
 ```shell
 curl http://localhost:8080/api/v2/gateway/gateway_node/ex_server/ex_service/GetData -XPUT