minor update

Author: qingyang-hu

bson/vector.go

@@ -161,8 +161,10 @@ func binaryFromFloat32Vector(v []float32) Binary {
 }
 
 func binaryFromBitVector(bits []byte, padding uint8) Binary {
-	data := []byte{PackedBitVector, padding}
-	data = append(data, bits...)
+	data := make([]byte, len(bits)+2)
+	data[0] = PackedBitVector
+	data[1] = byte(padding)
+	copy(data[2:], bits)
 	return Binary{
 		Subtype: TypeBinaryVector,
 		Data:    data,