Mongoose v4.8.7 warns about Promise AFTER setting it

Why is Mongoose showing the deprecated warning after I have set the promise library?

Countless posts (example #1, example #2, etc.) say to set mongoose.Promise = global.Promise; to resolve this warning. I have even done it myself in the past! However, nothing I do prevents Mongoose from complaining about the promise library:

(node:54561) DeprecationWarning: Mongoose: mpromise (mongoose's default 
promise library) is deprecated, plug in your own promise library instead: 
http://mongoosejs.com/docs/promises.html

I'm using v4.8.7 with the following code:

var bodyParser  = require('body-parser'),
    config      = require('./config'),
    data        = require('./data'),
    express     = require('express')
    mongoose    = require('mongoose'),
    routes      = require('./routes');

mongoose.Promise = global.Promise;

var db  = mongoose.connection;
var app = express();

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

app.use(routes);

db.once('open', function() {

    console.log('Database connected!');

    data.seeds.doSeed(function(){

        app.listen(3000, function() {
            console.log('Mongo example listening on port 3000!');
        });
    });
});

mongoose.connect(config.db.uri, config.db.options);

via G. Deward