Change `data-role` attribute for Select2TagsWidget.
Change `data-role` attribute for Select2TagsWidget.

Values from `data-tags` are picked up only when `data-role` is set to
`select2-tags` (according to `form.js`).

jmagnusson/flask-admin,rochacbruno/flask-admin,jmagnusson/flask-admin,flask-admin/flask-admin,rochacbruno/flask-admin,rochacbruno/flask-admin,flask-admin/flask-admin,rochacbruno/flask-admin,flask-admin/flask-admin,flask-admin/flask-admin,jmagnusson/flask-admin,jmagnusson/flask-admin