fix: remove workaround for escaping doctype

This was fixed in marked 0.4.0
markedjs/marked#354 (comment)

lib/renderer.js

@@ -104,10 +104,7 @@ function tokenizeEditor(editorElement: HTMLElement, preElement: HTMLPreElement):
  * @return {Node} the html template node containing the result
  */
 function internalRender(markdownText: string): Node {
- // Remove the <!doctype> since otherwise marked will escape it
- // https://github.com/chjj/marked/issues/354
- let text = markdownText.replace(/^\s*<!doctype(\s+.*)?>\s*/i, '');
- let html = DOMPurify.sanitize(marked(text, { breaks: true }));
+ let html = DOMPurify.sanitize(marked(markdownText, { breaks: true }));
  let template = document.createElement('template');
  template.innerHTML = html.trim();
  return template.content.cloneNode(true);