Merge pull request vega#2304 from vega/v5.9.1

v5.9.1

Fix kde2d documentation. (vega#2229)

Add build files.

Fix rollup in vega-functions package.json.

Update docs build files.

Bump vega-typings version.

Update docs build files.

Update histogram.md

Update build files.

Fix "mis[s]ing" typo in Window docs.