digest: use digest.Parse over ParseDigest

Signed-off-by: Stephen J Day <stephen.day@docker.com>

registry/storage/blobstore.go

@@ -145,7 +145,7 @@ func (bs *blobStore) readlink(ctx context.Context, path string) (digest.Digest,
 		return "", err
 	}
 
-	linked, err := digest.ParseDigest(string(content))
+	linked, err := digest.Parse(string(content))
 	if err != nil {
 		return "", err
 	}

registry/storage/vacuum.go

@@ -29,7 +29,7 @@ type Vacuum struct {
 
 // RemoveBlob removes a blob from the filesystem
 func (v Vacuum) RemoveBlob(dgst string) error {
-	d, err := digest.ParseDigest(dgst)
+	d, err := digest.Parse(dgst)
 	if err != nil {
 		return err
 	}