DOC: updated version: 2.1_beta1
DOC: updated version: 2.1_beta1

Former-commit-id: 0c6d1499de7d254e98716810847726ec686884d6 [formerly 5b44e259acfef19bad7e87c0a43778c23aa86fcd]
Former-commit-id: 9e26fc383cfd745f731212d92448f3b17f46efff
Former-commit-id: a29e98a214ec12a641056c1ddd2673d1e712b085
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox