Add TS 2.7 compatibility. Fixes #3862. 
Add TS 2.7 compatibility. Fixes #3862. 
uwdata/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite