Update katex to v0.7.0

As v0.7.0 has some problems with its bower distribution, the files included
in this commit are taken from the npm release instead.

bower_components/katex/bower.json

@@ -1,6 +1,6 @@
 {
   "name": "KaTeX",
-  "version": "0.6.0",
+  "version": "0.7.0",
   "main": [
     "dist/katex.min.js",
     "dist/katex.min.css"

bower_components/katex/dist/README.md

@@ -16,8 +16,8 @@ KaTeX supports all major browsers, including Chrome, Safari, Firefox, Opera, and
 You can [download KaTeX](https://github.com/khan/katex/releases) and host it on your server or include the `katex.min.js` and `katex.min.css` files on your page directly from a CDN:
 
 ```html
-<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.5.1/katex.min.css">
-<script src="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.5.1/katex.min.js"></script>
+<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.6.0/katex.min.css">
+<script src="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.6.0/katex.min.js"></script>
 ```
 
 #### In-browser rendering