chore: upgrade docker distribution from 2.7.1 to 2.8.0 (#328)

Fixes a low-severity security vulnerability:
GHSA-qq97-vm5h-rrhg

go.mod

@@ -73,6 +73,7 @@ require (
 	github.com/dhui/dktest v0.3.9 // indirect
 	github.com/dlclark/regexp2 v1.4.0 // indirect
 	github.com/docker/cli v20.10.12+incompatible // indirect
+	github.com/docker/distribution v2.8.0+incompatible // indirect
 	github.com/docker/docker v20.10.12+incompatible // indirect
 	github.com/docker/go-connections v0.4.0 // indirect
 	github.com/docker/go-units v0.4.0 // indirect

go.sum

@@ -378,8 +378,9 @@ github.com/docker/cli v20.10.12+incompatible h1:lZlz0uzG+GH+c0plStMUdF/qk3ppmgns
 github.com/docker/cli v20.10.12+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
 github.com/docker/distribution v0.0.0-20190905152932-14b96e55d84c/go.mod h1:0+TTO4EOBfRPhZXAeF1Vu+W3hHZ8eLp8PgKVZlcvtFY=
 github.com/docker/distribution v2.7.1-0.20190205005809-0d3efadf0154+incompatible/go.mod h1:J2gT2udsDAN96Uj4KfcMRqY0/ypR+oyYUYmja8H+y+w=
-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 v20.10.7+incompatible/go.mod h1:eEKB0N0r5NX/I1kEveEz05bcu8tLC/8azJZsviup8Sk=
 github.com/docker/docker v20.10.9+incompatible/go.mod h1:eEKB0N0r5NX/I1kEveEz05bcu8tLC/8azJZsviup8Sk=
 github.com/docker/docker v20.10.12+incompatible h1:CEeNmFM0QZIsJCZKMkZx0ZcahTiewkrgiwfYD+dfl1U=