test case: http://tangrams.github.io/differ/?1=https://github.com/tangrams/bubble-wrap/blob/sensescape/shields/bubble-wrap.yaml&2=https://github.com/tangrams/bubble-wrap/blob/sensescape/shields/bubble-wrap.yaml&lib1=0.10&lib2=https://precog.mapzen.com/tangrams/tangram/placement-min-ratio/dist/tangram.debug.js&go
