Properly format the hash

Currently the readme reads:

```
or, you can provide a hash of user/password pairs and have the auth file dynamically
created:

  node[:geminabox][:auth_required] = {'user1', 'secret'}
```

I'm guessing that comma should be a =>.
adding rubygems proxy flag
Update default.rb
Update default.rb
add name attribute to avoid chef error
Remove explicit ubuntu support line