Update wd40 to 0.1.0

Previously the version specification was "*", which probably makes sense in
that we control wd40, so if we're updating it, it's probably because we want
to use it. OTOH, I want to actually document in the custard repository when
wd40 is changed in an important way.

I've published it to NPM.

Since this only changes a development dependency it can be merged without prejudice.