fix (scripts/release-version.ps1): fix windows build

fix reflects changes made in commit
https://github.com/coreos/etcd/commit/7670c85d70f87d1749d6a49a202c5067a55d2748
fix(build.ps1): not required to be admin to run build in windows

mklink /D in windows requires elevated privilege (Runas Administrator),
'/J' to create a directory junction point runs with user privilege
use an explicit fully qualified path for junction target
Merge pull request #434 from rwindelz/master

fix (scripts/release-version.ps1): fix windows build