Severity "critical" not supported

[pablocoberly]

The snyk azure devops task supports a severity threshold of "critical", however this Gradle task seems to only support high, medium, low, or empty.

If you set:

    severity = 'critical'

You get a Gradle build error:

> Severity should either high|medium|low or empty

Is it possible to add "critical" as a supported severity threshold or was critical not included for a specific reason?