Improvement: Support Snyk NPM Repositories

[emmercm]

I believe the current Badgen Snyk support is for GitHub repositories only, e.g.:

https://snyk.io/test/github/{username}/{repo}/badge.svg

but Snyk's official badges also support NPM repositories, e.g.:

https://snyk.io/test/npm/{name}/badge.svg

I'd love to embed the NPM one in my READMEs as it is more relevant to my end-user than the state of vulnerabilities fixed in the code trunk.

Documentation: https://docs.snyk.io/integrations/git-repository-scm-integrations/github-integration#github-badges

Thank you!