Prepare datapackage for rOpenSci drat builds

[gothub]

The datapackage package depends on the redland package, so is not included in the automatic drat builds, with the related issue in the drat.builder repo that mentions a problem with building packages
'deep' directory structures (i.e. redland): https://github.com/richfitz/drat.builder/issues/9. Ensure that datapackage builds properly in preparation for the resolution to the drat.builder issue.