travis: build sphinx docs
travis: build sphinx docs

Former-commit-id: 01a7a9e7fecdd099fc49a8625b67204d953d45d4
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox