Update for internal packages

**Dependent on [PR 27](https://github.com/zopaUK/bozo/pull/27) in Bozo**

Add a step in the Nuget dependency resolver to update the internal packages to a new version.

The new version is taken from the `bozorc.rb` file for each project. The `bozorc.rb` should looks like this:

    resolve_dependencies_with :nuget do |n|
      n.source '\\\\path\\to\\nuget\\repository'
      n.packages_to_update ({ "Package1" => "4.22.1", "Package2" => "4.22.1", "Package3" => "4.22.1" })
    end

Third line above is the new stuff.

Once this is merged, then you can just update the `bozorc.rb` file in each project and run `bin/bozo prepare`. That would take care of updating all references to each package.