Upgrade topojson to 1.6.8

They actually removed the their license header from the js file they release and now directly support loading as an AMD module (we previously tweaked this file I believe and are now using it as-is).
Changes after review.
More fixes to license information.
Merge remote-tracking branch 'origin/master' into upgrade-topojson

Conflicts:
	CHANGES.md
Merge pull request #1644 from AnalyticalGraphicsInc/upgrade-topojson

Upgrade topojson to 1.6.8