Updating non working usage example of Git.clone

Git.clone expects a name to be present as the second param. The `Git.clone(uri, opts)` is not supported (by Git, Base or Lib).

`lib/git.rb`

    def self.clone(repository, name, options = {})
      Base.clone(repository, name, options)
    end

`lib/git/lib.rb`

    def clone(repository, name, opts = {})
    ...

`lib/git/base.rb`

    def self.clone(repository, name, opts = {})
    ...