Does not build on Windows

[0x263b]

Description

Running npm run build does not work on Windows due to not being able to execute "build-clean": "rm -rf css". (It would need to be rmdir css) And making a Windows specific script is not an option.

Steps to Reproduce

npm run build in Windows

Expected behavior

Generates css/bulma.css

Actual behavior

> bulma@0.4.0 build-clean D:\Code\bulma-0.4.0
> rm -rf css

'rm' is not recognized as an internal or external command,
operable program or batch file.

Possible solution

As far as I can tell it's unnecessary to delete the css directory before hand. Removing npm run build-clean from the build script fixes the issue.

[jgthms]

Try the master branch. It uses rimraf now.