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]>

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

go.sum

@@ -41,8 +41,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible h1:7qlOGliEKZXTDg6OTjfoBKDXWrumCAMpl/TFQ4/5kLM=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
-github.com/docker/distribution v2.7.1+incompatible h1:a5mlkVzth6W5A4fOsS3D2EO5BUmsJpcB+cRlLU7cSug=
-github.com/docker/distribution v2.7.1+incompatible/go.mod h1:J2gT2udsDAN96Uj4KfcMRqY0/ypR+oyYUYmja8H+y+w=
+github.com/docker/distribution v2.8.0+incompatible h1:l9EaZDICImO1ngI+uTifW+ZYvvz7fKISBAKpg+MbWbY=
+github.com/docker/distribution v2.8.0+incompatible/go.mod h1:J2gT2udsDAN96Uj4KfcMRqY0/ypR+oyYUYmja8H+y+w=
 github.com/docker/docker v1.13.1 h1:IkZjBSIc8hBjLpqeAbeE5mca5mNgeatLHBy3GO78BWo=
 github.com/docker/docker v1.13.1/go.mod h1:eEKB0N0r5NX/I1kEveEz05bcu8tLC/8azJZsviup8Sk=
 github.com/docker/go-connections v0.4.0 h1:El9xVISelRB7BuFusrZozjnkIM5YnzCViNKohAFqRJQ=