chore: Update portal URL (#2689)

.env

@@ -1,5 +1,5 @@
 REACT_APP_BACKEND_V1_GET_URL=https://json.excalidraw.com/api/v1/
 REACT_APP_BACKEND_V2_GET_URL=https://json.excalidraw.com/api/v2/
 REACT_APP_BACKEND_V2_POST_URL=https://json.excalidraw.com/api/v2/post/
-REACT_APP_SOCKET_SERVER_URL=https://excalidraw-socket.herokuapp.com
+REACT_APP_SOCKET_SERVER_URL=https://portal.excalidraw.com
 REACT_APP_FIREBASE_CONFIG='{"apiKey":"AIzaSyAd15pYlMci_xIp9ko6wkEsDzAAA0Dn0RU","authDomain":"excalidraw-room-persistence.firebaseapp.com","databaseURL":"https://excalidraw-room-persistence.firebaseio.com","projectId":"excalidraw-room-persistence","storageBucket":"excalidraw-room-persistence.appspot.com","messagingSenderId":"654800341332","appId":"1:654800341332:web:4a692de832b55bd57ce0c1"}'