deprecated push method

[beratetik]

native push method triggers mongoDB's $pushAll method. It's deprecated after MongoDB 3.6.2.
Need to replace with concat method => this.favorites = this.favorites.concat([id]);

node-express-realworld-example-app/models/User.js

Line 63 in ba04b70

this.favorites.push(id);

[klamping]

Nice, this fixed an error I had with not being able to follow users. Might see if I can open a PR with these updates (although it will probably never be accepted).