hljs class is not added to `<code>` wrapper

[artknight]

Just noticed that the hljs class is not being added to the <code> wrapper causing for some of the hljs styles not to work!

I fixed it by hacking easymde.js with this line

return '<pre><code class="hljs">' + (escaped ? _code : escape$1(_code, true)) + '</code></pre>\n';

But obviously this is not the way!