DOC: removed small spelling mistake
DOC: removed small spelling mistake

Former-commit-id: 9c1645eacb824f91536bb706f9cf7a8d3dc77a36 [formerly 80f0c4660773a82be67240e42033ca949d1cadfb]
Former-commit-id: cfb1e1720ade3c40f730d824976aadf8c2e60da8
Former-commit-id: efcb9f97b9ed1a3bb03d199c0410e09423d53edf
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox