Do not skip empty table rows.

[michbart]

I've modified some tests so they are correct and passing when https://github.com/domchristie/turndown/pull/311 is accepted. I will also update package.json in this pull request again when the Turndown pull request is accepted.

[guyplusplus]

Interesting : when running test script via npm, empty rows do not trigger the 'tr' filter, hence test pass. But on browser (firefox, chrome), empty rows trigger the 'tr' flter. The output is then different. I am trying to figure out...