fix issue where repos importing this Gruntfile need to have freedom(-for-*)* packages installed

I'm moving `turn-relay` to use the new `uproxy-lib` stuff. I want it to use `freedom-for-uproxy.js` and am removing the direct dependencies on `freedom`, `freedom-for-chrome`, and `freedom-for-firefox`. In the `require` statements' current locations I still need to have those packages available or the import fails.

This is a rare case where symlinking masks an issue because typically when you symlink that folder has all its dependencies in _its_ `node_modules/`. That's the case when installing by NPM, though.