Test this extension with CKAN 2.8 and test it. - [x] Do a manual test to check if it's working - [x] Create a DataJSON harvest source - [x] Run the harvestr job - [x] Analize if the harvested datasets is what we expect. - [x] Import tests from [datajson fork](https://github.com/datopian/ckanext-datajson/tree/f1dad77d9028262a53ce1f854fbaab3aae5b24ef/ckanext/datajson/tests) - [x] Add CircleCI configuration (re-use from datopian) FYI @adborden