Bump github.com/docker/distribution

Bumps [github.com/docker/distribution](https://github.com/docker/distribution) from 2.7.1+incompatible to 2.8.0+incompatible.
- [Release notes](https://github.com/docker/distribution/releases)
- [Commits](https://github.com/docker/distribution/compare/v2.7.1...v2.8.0)

---
updated-dependencies:
- dependency-name: github.com/docker/distribution
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/github.com/docker/distribution/reference/reference.go

@@ -205,7 +205,7 @@ func Parse(s string) (Reference, error) {
 	var repo repository
 
 	nameMatch := anchoredNameRegexp.FindStringSubmatch(matches[1])
-	if nameMatch != nil && len(nameMatch) == 3 {
+	if len(nameMatch) == 3 {
 		repo.domain = nameMatch[1]
 		repo.path = nameMatch[2]
 	} else {