Fix the sed(1) invocation used to process git-svn-id not to use "\s"
that is a GNU-ism and is not supported by NetBSD sed. As a result,
this call did not work properly and make_version did output the full
git-svn-id line rather than the revision.
ASTERISK-29852
Change-Id: Ie4b406e2748920643446851a0a252a4ca7245772