fix: actually add a type property to the def token (#2002)

Hmm I think I modified the wrong file (`lib/marked.js`) in the previous PR (see #2001) , this should be the right one ! Sorry for that.

src/Tokenizer.js

@@ -347,6 +347,7 @@ module.exports = class Tokenizer {
       if (cap[3]) cap[3] = cap[3].substring(1, cap[3].length - 1);
       const tag = cap[1].toLowerCase().replace(/\s+/g, ' ');
       return {
+        type: 'def',
         tag,
         raw: cap[0],
         href: cap[2],