Revert inaccurate description from https://github.com/vega/vega-lite/pull/3180
Revert inaccurate description from https://github.com/vega/vega-lite/pull/3180

cc: da39a3ee5e6b4b0d3255bfef95601890afd80709@domoritz

uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite