Add a shorthand syntax for the Npm task

[decoyjoe]

It would be nice for the Npm task to support a shorthand syntax to make multiple Npm tasks in a whiskey.yml more concise.

From:

- Npm:
    Command: install

- Npm:
    Command: audit

- Npm:
    Command: run
    Argument: build

To:

- Npm: install

- Npm: audit

- Npm: run build

[pnstickne]

Also applies for PS tasks. There is some structure to have to separate though.