Remove `git br` alias

I almost never use `git branch`.
Add `g pr` alias for `hub pull-request`
Bundle vim-ruby/vim-ruby

vim-ruby is where Vim's support for Ruby comes from - file type
detection, syntax highlighting, etc. Vim bundles vim-ruby, but the
GitHub project is always ahead of what's released with Vim.
Don't use suffix flag for zsh compadd command

* Fixes an issue where tab completing specs that start with the same
words(s) makes tab completion freak out and stop working.

* The con is that we'll see "_spec.rb" in the output, like:

```zsh
$ rspec spec/models/
models/calendar_spec.rb
models/event_closer_spec.rb
...
```