Allow custom username

[albertogasparin]

Currently you are using os.hostname() as username for slack messages.
As we don't want to make it public, could you add an option to override it?
We have also tried setting a default on the Slack webhook but that gets ignored.
Thanks

[mattpker]

This feature has been added and published to npm. Please run pm2 install pm2-slack to update to the newest version and then run pm2 set pm2-slack:username theusername to set the username you want.

Please let me know if you experience any issues with this new feature. Thanks!