fix eslint config

.eslintrc.json

@@ -9,6 +9,6 @@
       }
     ],
     "no-console": "off",
-    "no-underscore-dangle": ["on", { "allow": ["_id"] }]
+    "no-underscore-dangle": ["warn", { "allow": ["_id"] }]
   }
 }

app.js

@@ -44,7 +44,6 @@ app.use((req, res) => {
 });
 
 // handle errors
-
 app.use((err, req, res, next) => {
   if (err.name === 'ValidationError') {
     res.status(400);