[HTML-CSS] square root top line is too close to the number below

Created by: karoltarasiuk

Issue Summary

Square root top line is too close to the number below. I have also replicated the bug on latest develop branch using unpacked/MathJax.js.

Steps to Reproduce

Simple go here: https://docs.staging.learnosity.com/demos/isolation/mathjax/260rendering.php

Or check this sample page:

<!DOCTYPE html>
<html>
<head>
<title>MathJax TeX Test Page</title>
<!-- Copyright (c) 2010-2015 The MathJax Consortium -->
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1">

<script type="text/x-mathjax-config">
MathJax.Hub.Config({
    tex2jax: {inlineMath: [["$","$"],["\\(","\\)"]]}
});
</script>
<script type="text/javascript" src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS_HTML-full"></script>

</head>
<body>

<p>
When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are
$$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$
</p>
<p>
text around \(\frac{\sqrt{123}}{123}\) text around
</p>
<p>
$\frac{\sqrt{123}}{123}$
</p>

</body>
</html>

Technical details

MathJax Version: develop - latest commit: 0740dd47
Client OS: MaxOS
Browser: Chrome 48