* Any reason to use `https:` over `git:`?  I personally always use the git protocol and I'm under the impression it's faster.  (I haven't actually benchmarked it though).  We tend to use the git protocol [in our gemfiles](https://github.com/rspec/rspec-core/blob/9362e65fc358a60545ea58912c0885657bb61207/Gemfile#L10) though.
* I think we'll want this to checkout the appropriate branch (e.g. 2-14-maintenance, 2-99-maintenance or master).  Currently we have that listed in the `Gemfile` (as the `:branch`) but that'll be kinda a pain to parse out.  Instead, what do you think about having a `maintenance-branch` file that lists the branch and then we can read that from `Gemfile` and from this script.
* I'm not sure if the `--depth` option will work when you are checking out a branch.  Do you know?