added setup script in package.json, required to get eslint to work with arc
added setup script in package.json, required to get eslint to work with arc

Reviewers: arik

Reviewed By: arik

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D6108

BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS