chore(deps): 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](distribution/distribution@v2.7.1...v2.8.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

go.mod

@@ -10,7 +10,7 @@ require (
 	github.com/asaskevich/govalidator v0.0.0-20200428143746-21a406dcc535
 	github.com/cpuguy83/go-md2man/v2 v2.0.0 // indirect
 	github.com/creack/pty v1.1.10 // indirect
-	github.com/docker/distribution v2.7.1+incompatible // indirect
+	github.com/docker/distribution v2.8.0+incompatible // indirect
 	github.com/docker/docker v1.13.1
 	github.com/docker/go-connections v0.4.0
 	github.com/docker/go-units v0.4.0 // indirect