Use the new `bin_mid` from vg 2.4.0  (fixes #695)
Use the new `bin_mid` from vg 2.4.0  (fixes #695)

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