Support build on Windows

[gtnsimon]

Currently it is not possible to run npm run build on Windows because scripts use OS-specific commands listed below:

• orejime/package.json

  Line 23 in 61612c7

  "copy-scss": "cp src/scss/orejime.scss dist/orejime.scss",

• orejime/package.json

  Line 25 in 61612c7

  "clean-build": "rm -Rf ./dist/orejime.{js,css,scss} && rm -Rf ./lib && rm -Rf ./es",

It would be great to have the ability to run it on Windows to propose changes.

I can address a PR for this feature.

[felixgirault]

I didn't know about shx, it seems to work like a charm 👍
Thank you for this fix, I just merged the PR!