Fix vet warning

pkg/archive/archive_test.go:496: arg changes for printf verb %s of wrong type: []archive.Change

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

pkg/archive/archive_test.go

@@ -493,7 +493,7 @@ func TestTarWithBlockCharFifo(t *testing.T) {
 		t.Fatal(err)
 	}
 	if len(changes) > 0 {
-		t.Fatalf("Tar with special device (block, char, fifo) should keep them (recreate them when untar) : %s", changes)
+		t.Fatalf("Tar with special device (block, char, fifo) should keep them (recreate them when untar) : %v", changes)
 	}
 }