Deal with build-storybook being an alias to another script

[tmeasday]

This fairly uncontroversial setup:

https://github.com/planningcenter/design/blob/2531a8ab7437b96581c310c3a8fee82fd1c7820e/package.json#L42-L43

Stuffs us up because the -o flag doesn't end up getting passed through to the build script.

Related to #78

[ndelangen]

I don't see a -o in the linked example?

[tmeasday]

We add a -o $tmpdir flag and I guess the way npm/yarn works it didn't end up passing through to the final command.

[ndelangen]

The user can use the --build-script-name to point the cli to the correct script OR they could use yarn (which does passes though any flags) OR they could use something like:

    "build": "build-storybook",
    "build-storybook": "npm run build --",