add prettier to backend

backend/src/app.ts

@@ -1,11 +1,11 @@
-import express from 'express';
-const app = express();
-const port = 3000;
+import express from 'express'
+const app = express()
+const port = 3000
 
 app.get('/', (req, res) => {
-  res.send('Hello World!');
-});
+  res.send('Hello World!')
+})
 
 app.listen(port, () => {
-  return console.log(`Express is listening at http://localhost:${port}`);
-});
+  return console.log(`Express is listening at http://localhost:${port}`)
+})