Specify height for SVG elements (#1252)

* Specify height for SVG elements

I ran into an issue where a low-specificity CSS rule elsewhere on the page was overriding the KaTeX SVG height, rendering fraction lines invisible. Does this seem like a reasonable addition to the style sheet?

* Inherit instead of 100%.

src/katex.less

@@ -445,6 +445,7 @@
         display: block;
         position: absolute; // absolute relative to parent
         width: 100%;
+        height: inherit;
 
         // We want to inherit colors from our environment
         fill: currentColor;