add optional semicolon in html entities regex

and make non-capturing group out of (\w+) that was not used in the function
(only the entire surrounding group is used as a whole)
The semicolon is outside of the capturing group so the input to the
function is the same as before.
See this comment:
https://github.com/chjj/marked/pull/592/files/2cff859#r70888592

lib/marked.js

@@ -1095,7 +1095,7 @@ function escape(html, encode) {
 
 function unescape(html) {
 	// explicitly match decimal, hex, and named HTML entities 
-  return html.replace(/&(#(?:\d+)|(?:#x[0-9A-Fa-f]+)|(\w+))/g, function(_, n) {
+  return html.replace(/&(#(?:\d+)|(?:#x[0-9A-Fa-f]+)|(?:\w+));?/g, function(_, n) {
     n = n.toLowerCase();
     if (n === 'colon') return ':';
     if (n.charAt(0) === '#') {