Update PULL_REQUEST_TEMPLATE.md (#3448)
Update PULL_REQUEST_TEMPLATE.md (#3448)

* Update PULL_REQUEST_TEMPLATE.md

cc: da39a3ee5e6b4b0d3255bfef95601890afd80709@domoritz

* Update PULL_REQUEST_TEMPLATE.md

* Update PULL_REQUEST_TEMPLATE.md

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