title text generated by toc helper is not escaped

[unnamed42]

For example, I have:

## Get modulus of (1<<s)-1

HTML in main document is correct:

<h2 id="get-modulus-of-1-s-1">Get modulus of (1&lt;&lt;s)-1</h2>

But HTML generated by toc() helper is not escaped:

<li class="toc-item toc-level-2">
    <a class="toc-link" href="#get-modulus-of-1-s-1">
        <span class="toc-text">Get modulus of (1<<s)-1</span>
    </a>
</li>

By the way, I'm using hexo-renderer-markdown-it as my markdown renderer.

[NoahDragon]

We could move the discuss to the PR #2437 .