Improve text-node support

[rigor789]

Consider this example:

<label>Some Text</label>

Some Text is a text-node, which can't be added as a child element in {N}, so we replace the parent element. This works fine for labels, but due to the current implementation, this has undesired side effects:

<button>Some Text</button>

gets rendered as a Label.

The lines to blame are here:
https://github.com/rigor789/nativescript-vue/blob/311c5026aec3452f9cdf11e567d3ad3b1d59227f/nativescript-vue/platform/nativescript/renderer/NativeScriptRenderer.js#L56-L59

[rigor789]

This has been fixed in 8da45a1