Node 12 deprecation of OutgoingMessage.prototype._headers is deprecated
I am not aware of which internals to update, so I feel I can't fix this myself.
In short, I get this deprecation warning after migrating to node 12 of our project:
```
OutgoingMessage.prototype._headers is deprecated
```
I guess usage if this must be updated before next node LTS version will go live anddeprecated `_headers` property will be removed at all.