Fix "argument_count" issue in docker-grype/pygrype/vulnerabilities.py

[dallinb]

Function add has 5 arguments (exceeds 4 allowed). Consider refactoring.

https://codeclimate.com/github/cbdq-io/docker-grype/docker-grype/pygrype/vulnerabilities.py#issue_62b4c80f3ad9180001000023