Quick and easy fix: backwards logic in build scripts

[exscape]

The platform-specific build scripts all contain the same error:

if [ ! -d "dist" ]; then
    rm -rf dist
fi

# Cleanup old build files
if [ ! -d "build" ]; then
    rm -rf build
fi

This only removes the directories when they already don't exist, so the negation operator shouldn't be there.

[Pectojin]

Ah, I hadn't noticed. I've fixed it in latest commit, thanks :slightly_smiling_face: