Don't publish binaries for git tags

[mattficke]

Pushing a commit with [publish binary] along with a tag referencing that commit leads to build failures, since Travis will run duplicate build jobs that both try to publish their binaries to the same place. Whichever one finishes first will succeed, the other will fail. This causes many commits to be incorrectly flagged as failing CI, though it doesn't cause really any substantive problems beyond that.

This issue was reported in mapbox/node-cpp-skel#108, and seems to have been fixed with mapbox/node-cpp-skel#139, so I think the next steps are:

• add the node-cpp-skel updates to carmen-cache/scripts/publish.sh
• make sure it works
• merge

cc @springmeyer @apendleton

[springmeyer]

👍 @mattficke - would love testing help to confirm the fix in mapbox/node-cpp-skel#139 is correct/works. /cc @mapbox/maps-api

[springmeyer]

Noting that this still applies. The current workarounds are:

• Don't attempt to publish with the same commit as you tag
• If you do and you see publish failures, ignore them as long as they are truly failures due to inadvertent double-publish attempt

But ideally we'd fix this to avoid potential confusion, so the above plan still applies to try pulling over the latest fixes from node-cpp-skel's publish.sh and see if that resolves the potential gocha.