Update build scripts

[slifty]

Task

Description

Our build scripts all have the same bug, which is described tvkitchen/appliances#85 and also explained in this StackOverflow question.

We ultimately want to wipe out the babel output directory(ies) before transpiling, since babel won't properly clean up dead files nor will it properly rename files in case-insensitive operating systems if the only change was a case change.