DataChart cannot render bars when data includes a negative value.

Expected Behavior

• If data has some negative value, the chart will have a zero line guide as default.
• I wish we can custom attributes(colors) of negative value.

Actual Behavior

• A chart shows nothing.

URL, screen shot, or Codepen exhibiting the issue

Steps to Reproduce

https://v2.grommet.io/datachart?c=BQSgBAvAfGDeBQYwGMD2A7AzgFzAEwENsDIwBtWfIgUwC4wByAJgAZWBaFgDndYYBowBALaoArumz1eYAL6DKhbHUasO3XgEYBQ0RKlgALAHY5CqsvrM2LTjyZMdI8ZPoBmN3IC6AbkRgAJ2psMQD0MGB-JAAeABEiAgBhAAsCAOwopAsCCFglAllMpExqAIBLakxcsgYlah0GZ30GL0KsrORU9OqirMoABwDUftLsAE8rJskdcZGrABsy9HrBYYJkMvGrYWo8MrFhGeSy5ABrZcxMKwAPTGECefmdIYk8M16kAaGR9InGKewMzGc0Y-VQS0BgjBEKsODSRxO50qV0YOz2BwYcl6rUyAHooP4QH5ZEA

Your Environment

• Grommet version: 2.4.0
• Browser Name and version: Chrome
• Operating System and version (desktop or mobile): Mac