app.use 중복 수정

backend/app.js

@@ -39,8 +39,6 @@ app.use(express.static(path.join(__dirname, "public")));
 app.use("/api/books", bookRouter);
 app.use("/api/login", loginRouter);
 
-app.use('/api/books', bookRouter);
-
 //app.use('/users', usersRouter);
 
 // catch 404 and forward to error handler