add findGameById to ServerApp

fh.fd.ci.server/src/main/java/de/fd/fh/ServerApp.java

@@ -57,6 +57,7 @@ public class ServerApp
         get("/users/:user_id", userController::getUser);
 
         post("/games", gameController::createGame);
+        get("/games/:game_id", gameController::findGameById);
 
         get("/hello", (req, res) -> "Hello World");