Add version information to edges of berks viz

This branch patch successfully adds version information to the edges of the nodes in `berks viz`.

Unfortunately, the berkshelf README doesn't include information on how to run the tests and I am new to ruby so I don't know how to get started. If that information is added somewhere, and this functionality is wanted, I'd be happy to clean this up to get it included upstream.
So... If we add a hash instead of an array:

```ruby
@nodes[a].add(b => version)
```

Then the loop below could become more semantic:

```ruby
adjacencies(node).each do |name, version| 
  if version == Solve::DEFAULT_VERSION
    out << %|  "#{node}" -> "#{edge[0]}" [ fontsize = 10 ]\n|
  else
    out << %|  "#{node}" -> "#{edge[0]}" [ fontsize = 10, label = " #{version}" ]\n|
  end
end
```