title: Highlight active line in CodeMirror
body: <p>Looking at the <a href="https://codemirror.net/demo/activeline.html" rel="nofollow noreferrer">demo</a> here, I downloaded the <code>active-line.js</code> file and included it in my HTML as shown in the demo but nothing happens. I included it like so:</p>
  
  <pre><code>&lt;script src="/js/codemirror.js"&gt;&lt;/script&gt;
  &lt;script src="/js/sql.js"&gt;&lt;/script&gt;
  &lt;script src="/js/active-line.js"&gt;&lt;/script&gt;
  &lt;link rel="stylesheet" type="text/css" href="/css/codemirror.css"&gt;
  </code></pre>
  
  <p>This is how I initialise CodeMirror:</p>
  
  <pre><code>&lt;script&gt;
      CodeMirror.fromTextArea(document.getElementById("maple_code"), {
          lineNumbers: true,
          mode: "text/x-mysql"
      });
  &lt;/script&gt;
  </code></pre>
  
  <p>Syntax highlighting and line numbers work as they should except the active line highlighting. Do I need to tweak anything in the options as well?</p>