BUGFIX: Used node-gd fixed for building on Mac

Currently no-one with fresh mac will be able to `npm install` in `gcd-client` - node-gd from this repo is not buildable on mac beacause bad CPP INCLUDE_PATH which was fixed in mikesmullin/node-gd@b834e8b7 (and extended with MacPorts support in mikesmullin/node-gd@402525ad).Because this was not released as a packaged on npmjs, we need to depend on specific commit temporarily.

This change should be temporary - we should check after a month or so if this was finally released to npmjs.

@crudo or @opichals pls review and create a jira ticket for me - I will fix commit message and PR title. Thx!