require git only when installing via gem or bundler

After talking with @adrienthebo, distro packages of r10k should have git as a
runtime dependency. If they don't, they are broken and should be fixed
new URL for the make module
Merge pull request #23 from tampakrap/make_new_location

new URL for the make module
Merge pull request #22 from tampakrap/require_git

require git only when installing via gem or bundler
add support for yum provider
rebase from master, spec fixes
merge fixes