New mongodb driver will connected failed

Code
```
const db = require('monk')('mongodb://127.0.0.1:27017/main');

db.then(() => {
console.log('Connected correctly to server');
}).catch(() => {
console.log('Connected failed');
});

```

mongodb driver 3.6.2
`Connected correctly to server`

mongodb driver 3.6.3
`Connected failed`

Reproduce the supplied Monk connection snippet with MongoDB driver versions 3.6.2 and 3.6.3, then inspect Monk’s connection handling and existing entry points. Done means the version change is explained and the connection behavior is fixed or the supported driver compatibility is clearly recorded.

Written by the indexing model from the issue text.