Change function() in mongoose.connection.once to arrow-notation

src/libs/db/mongoose.js

@@ -11,7 +11,7 @@ module.exports = () => {
     log.debug(`Connecting to MongDB on URI ${mongoUri}`);
     const db = mongoose.connect(mongoUri);
 
-    mongoose.connection.once('open', function() { log.info("Mongo DB connected!"); });
+    mongoose.connection.once('open', () => { log.info("MongoDB connected"); });
 
     return db;
 };