RIMRAF is MISSING

[lsuhadolnik]

https://github.com/microsoft/pxt/blob/195915f5c5f706007729b5fbafea4081c8c0248b/pxt-cli/package.json#L30

When using link command, it fails due to missing package. Must add the RIMRAF dependancy

"dependencies": {
  "rimraf": "^3.0.2"
}