ref: https://github.com/helm/helm/security/advisories/GHSA-c38g-469g-cmgx



* Skip invalid chart versions when reading the repository index file or
  when programmatically adding a chart version.
* Adds semver validation and strips non-printable characters and
  normalizes spaces for string fields in Metadata.Validate()
* Fixes a unit test that was pulling a remote repo.  Now uses a local
  repo.
* Fixes ignored error in repo update command
Signed-off-by: Adam Reese <adam@reese.io>