linkedom adaptor needs splitText polyfill (for TeX pre-processing)

[pkra]

For a side project I was building a quick nodejs demo using linkedom.

I noticed that processing a page with TeX in it fails due to https://github.com/WebReflection/linkedom/issues/156.

Adding the naive implementation from the issue seemed enough to fix it.

[dpvc]

Thanks. I'll look into adding the implementation given there.