configure: fix a stale sheep version output

This fixes a possible stale out of 'sheep -v'

Reviewed-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
sheepdog stable release v0.7.6-rc2

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>