Fix for network.rb options object not being converted correctly

Hi there

I was trying to create a secondary adapter for the vagrant virtualbox provider and consistently failing. After some help from one of our ruby guys, we realised that the method called expects a hash and it actually receives and array with a hash inside. This pull request fixes this. 

Example (Vagrantfile):
<pre>
  config.vm.provider "virtualbox" do |v|
    v.network_adapter 2, :bridged, { auto_config: true }
  end
</pre>