Fix the issue #51 that crashed the server on Linux.

With this slight change, a Node.js server that imports the module still works with Windows but now works too with Linux.

The hosts object contains a _store that's an object containing itself a _store. The access to the second one was missing.

{ _zone: '.',
  _store: 
   { _store: { _store: [Object] },  <----
     _zone: '.',
     _max_keys: undefined,
     _ttl: { length: 0, root: undefined, _comparator: [Function] } },
  purge: [Function] }

It would solve the issue #51 and it would be great to push it to NPM as well.

Thanks.