Fixes /swarm/join endpoint documentation

The JSON payload given in the API documentation is wrong, fixing it.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>
(cherry picked from commit 97c9491b0d395dc923e8b4e335839662c17aff46)

docs/reference/api/docker_remote_api_v1.24.md

@@ -3663,7 +3663,7 @@ Join an existing new Swarm
 
     {
       "ListenAddr": "0.0.0.0:4500",
-      "RemoteAddr": "node1:4500",
+      "RemoteAddrs": ["node1:4500"],
       "Secret": "",
       "CACertHash": "",
       "Manager": false