replace 'git -C' with long version

The -C argument was introduced in git 1.8.4. CentOS 7.3 at the time of this commit provides v1.8.3.1.
see: https://git.kaarsemaker.net/git/commit/44e1e4d67d5148c245db362cc48c3cc6c2ec82ca/

Fixes #1004

automated install/basic-install.sh

@@ -135,7 +135,7 @@ fi
 is_repo() {
   # Use git to check if directory is currently under VCS, return the value
   local directory="${1}"
-  git -C "${directory}" status --short &> /dev/null
+  (cd ${directory} && git status --short) &> /dev/null
   return
 }