title: Deprecation warning when connecting to mongoose
body: <p>I'm connecting to a mongoose db, and I get a deprecation warning every time I try to connect.</p>
  <blockquote>
  <p>(node:14933) DeprecationWarning: current Server Discovery and
  Monitoring engine is deprecated, and will be removed in a future
  version. To use the new Server Discover and Monitoring engine, pass
  option { useUnifiedTopology: true } to the MongoClient constructor.</p>
  </blockquote>
  <p>I set <code>useUnifiedTopology</code> to true but I'm still getting the error. What am I doing wrong and how can I fix it?</p>
  <pre><code>const mongooseOptions = {
      useNewUrlParser: true,
      useCreateIndex: true,
      useFindAndModify: false,
      useUnifiedTopology: true,
  };
  
  const dbUrl = config.get('dbUrl');
  
  await mongoose.connect(dbUrl, mongooseOptions);
  </code></pre>