Use correct format verb
Fixes error when running make integration
$ make integration
+ integration
# github.com/docker/distribution
./blobs.go:70:9: Sprintf format %q has arg err.Cleanup of wrong type bool
make: *** [integration] Error 2
Fixes error when running make integration
$ make integration
+ integration
# github.com/docker/distribution
./blobs.go:70:9: Sprintf format %q has arg err.Cleanup of wrong type bool
make: *** [integration] Error 2