Users of `scratch-vm` do not need `playground` or `test` directories
installed as a npm package. If they need those directories they can
clone scratch-vm and do a local build. This saves downloading 42MB
(`playground`) and 4.4MB (`test`) when `npm install`ing `scratch-vm`.
Authenticate with NPM via .npmrc and publish the package version + "-[git sha]".
Remove vm and vm.min.js, they'll be built before the package is published to NPM and available on installation. When installing from git, the build step will run on npm install.