Make the type selector work for UPPER case elements

[stroiman]

The parser generates an error when parsing an element name in upper case, e.g., css.Parse("DIV"), which is working in a browser.

I use this library for gost, a headless browser with JavaScript execution, primarily for testing Go/HTMX stack.

HTMX generates such selectors, as it constructs them from tagName which returns uppercase tag names for HTML elements, resulting in selectors like DIV[id='root'].

I believe this should fix the issue, I hope that there are not aspects of the problem I'm unaware of.