Bump version to 0.3.1
Bump version to 0.3.1

sirex/datapackage-py,okfn/datapackage-py,datapackages/datapackage-py,okfn/datapackage-model-py,sirex/datapackage-py,okfn/datapackage-py,okfn/datapackage-model-py,datapackages/datapackage-py