textContent instead of innerText when available

[toothbrush7777777]

Fixes #88 and shouldn't affect the site (it falls back to using innerText if textContent is not supported).

Gecko does not support innerText, but Internet Explorer 9+ supports textContent, as does Chrome; see https://developer.mozilla.org/en-US/docs/Web/API/Node/textContent. DOM 3, DOM4, and DOM all define textContent, while innerText is a propriety Internet Explorer extension supported by Chrome and Opera for compatibility with MSIE.