Wrong colors + extra config

[fcecagno]

For anyone trying to use this in more recent versions of Rocket.Chat:

https://github.com/puzzle/prometheus-rocket-chat/blob/master/webhook.js#L36-L44

The colors good, danger and warning are no longer valid on Rocket.Chat, so you'll need to change it to black, red and yellow.

Also, you might get the error integration-scripts-disabled when trying to enable scripts in the integration. In order to fix that, make sure you do not have the environment variable FREEZE_INTEGRATION_SCRIPTS set (link).