Cannot find module 'timers' with webpack electron and karma

Since `bluebird 3.6.0` my unit tests does not work anymore.

The error is

```
Electron 6.0.11 (Node 12.4.0) ERROR
  Uncaught Error: Cannot find module 'timers'
  at webpack:///app/node_modules/bluebird/js/browser/bluebird.js:29:513 <- index.js:10450:289
```

Tested with `bluebird 3.5.5` and all works fine. `3.6.0` and upper thrown this error.

Any idea of the problem ? Thanks

