vendor: update buildkit to 8effd45b

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/Microsoft/hcsshim/internal/cow/cow.go

@@ -80,4 +80,6 @@ type Container interface {
 	// container to be terminated by some error condition (including calling
 	// Close).
 	Wait() error
+	// Modify sends a request to modify container resources
+	Modify(ctx context.Context, config interface{}) error
 }