allow to ignore cve for specific version

for example an unupgradable rails 2 would be `--ignore "2012-1098@~>2.3.18"`

It will be used for [organization-audit](https://github.com/grosser/bundler-organization_audit) where 1 set of rules is ran against all repos, making it necessary to ignore specific things that are safe on 1 version but not on another.

@postmodern