small fix for a node.js edge case

A Ractive instance's viewmodel should be 'applied' on initialisation, not just on render, so that `ractive.toHTML()` works correctly.

There's [one more test](https://github.com/ractivejs/ractive/blob/dev/test/samples/render.js#L447-L452) that's failing in node.js...
Fragment uses `get` so probably not directly. Probably inside `ViewModel` we can do the check, just need to figure out where...