Move back to upstream cluster2 package if our PR is merged

[missinglink]

Update package.json to remove the git:// url used as an interim solution until the upstream PR is closed, see commit: e3efeb6

The version number targeted for cluster2 MUST include this PR: cubejs/cluster2#86

[missinglink]

the upstream developers haven't responded for several months, unfortunately we will have to either fork this repo or continue using the github link to my commit hash.

[orangejulius]

Fixed in #585