fix(markdown): respect token attrs in code block

[Mister-Hope]

No description provided.

[Mister-Hope]

Some 3rd party markdown-it plugin about code blocks is effected with this bug.

We shall not just ignore token attrs as it might contain data- information and other attrs like id and class.

The following are markdown-it default renderer and we should no break it:

default_rules.code_block = function (tokens, idx, options, env, slf) {
  var token = tokens[idx];

  return  '<pre' + slf.renderAttrs(token) + '><code>' +
          escapeHtml(tokens[idx].content) +
          '</code></pre>\n';
};