Add explicit requirement for decorator module
Add explicit requirement for decorator module

pip-missing-reqs shows the following

Missing requirements:
magnum/api/validation.py:16 dist=decorator module=decorator

We should add that to our requirements as we have an import
that uses that package/module

Closes-Bug: #1490083
Change-Id: I8c9a4e1145fc99deddf92033e7e644c18dacc8b4
eshijia/magnum,openstack/magnum,ArchiFleKs/magnum,openstack/magnum,ArchiFleKs/magnum,annegentle/magnum,mjbrewer/testindex,Tennyson53/SUR,Tennyson53/SUR,dimtruck/magnum,eshijia/SUR,Tennyson53/magnum,Alzon/SUR,Tennyson53/magnum,annegentle/magnum,mjbrewer/testindex,mjbrewer/testindex,jay-lau/magnum,Alzon/SUR,eshijia/magnum,eshijia/SUR,dimtruck/magnum