wrong slugify result for some heading situation

[magicdawn]

e.g http://magicdawn.ml/clean-code-javascript/#/

there are some md code like

## **Variables**
### Use meaningful and pronounceable variable names

GitHub renders like

<h2>
 <a id="user-content-variables" class="anchor" href="#variables" aria-hidden="true">
 <svg>...</svg>
 </a>
 <strong>Variables</strong
</h2>

And docsify renders

<h2 id="strongvariablesstrong">
 <a href="#/#strongvariablesstrong" data-id="strongvariablesstrong" class="anchor">
 <span>
 <strong>Variables</strong>
 </span>
 </a>
</h2>

cause

results

Manually anchor broken