install_sct: conditionally install the pip prerelease (#1549)
install_sct: conditionally install the pip prerelease (#1549)


Former-commit-id: f9785e878a4457fac4207930e80047319295acfb
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox