Limit openpyxl to versions < 2.5 because of a bug on 2.5
Limit openpyxl to versions < 2.5 because of a bug on 2.5

See https://bitbucket.org/openpyxl/openpyxl/issues/977/version-25-breaks-with

datapackages/tabulator-py,frictionlessdata/tabulator-py,okfn/tabulator-py,okfn/datatable-py,frictionlessdata/tabulator-py