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

fix reflects changes made in commit
https://github.com/coreos/etcd/commit/7670c85d70f87d1749d6a49a202c5067a55d2748

scripts/release-version.ps1

@@ -2,6 +2,6 @@
 $VER=(git describe --tags HEAD)
 
 @"
-package main
-const releaseVersion = "$VER"
+package server
+const ReleaseVersion = "$VER"
 "@