Fix STUN server URL for jitsi/web (turns -> stun)

Discussed in #446 (Github Pull Request).

group_vars/matrix_servers

@@ -445,7 +445,7 @@ matrix_jitsi_jvb_auth_password: "{{ matrix_synapse_macaroon_secret_key | passwor
 matrix_jitsi_web_stun_servers: |
   {{
     [
-      'turns:' + matrix_server_fqn_matrix + ':5349',
+      'stun:' + matrix_server_fqn_matrix + ':5349',
       'stun:' + matrix_server_fqn_matrix + ':3478',
     ]
     if matrix_coturn_enabled