spec.bats: avoid using `git -C`
spec.bats: avoid using `git -C`

`git -C` is not present in git 1.8.3.1 shipped in CentOS 7

Signed-off-by: Akihiro Suda <10ddef0dea2a66ab193b07198faa879adcb213d8@hco.ntt.co.jp>

rhatdan/runc,opencontainers/runc,opencontainers/runc,estesp/runc,mikebrow/runc,xiaochenshen/runc,opencontainers/runc,mikebrow/runc,estesp/runc,kolyshkin/runc,xiaochenshen/runc,estesp/runc,kolyshkin/runc,rhatdan/runc,rhatdan/runc,dqminh/runc,opencontainers/runc,rhatdan/runc,mikebrow/runc,dqminh/runc,dqminh/runc,xiaochenshen/runc,kolyshkin/runc,kolyshkin/runc,dqminh/runc