Normal map generated by bum control bug

Hi!

Some users have reported a bug that causes normal maps generated by bump controls not being updated unless you modify the distance slider. This also affects when trying to invert some axis of normal maps. See: https://github.com/azagaya/laigter/issues/31

So, to workaround this issue, you can:

• Use 1.7 instead.
• Modify Distance control to update the map after you edited other controls, or checked invert checkbox.

This bug is fixed and it will work ok in 1.9.

Sorry for the inconvenience.