Fix release.sh sed of install.sh so we preserve tests against 'https://get.docker.io/'

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #3599 from tianon/fix-install-sed

Fix release.sh sed of install.sh so we preserve tests against 'https://get.docker.io/'