title: enable a disabled select when choose a value in another select tag
body: <p>I have these two select tag:</p>
  
  <pre><code>&lt;select&gt;
    &lt;option value="car"&gt;car&lt;/option&gt;
    &lt;option value="truck"&gt;truck&lt;/option&gt;
    &lt;option value="moto"&gt;moto&lt;/option&gt;
    &lt;option value="none"&gt;none&lt;/option&gt;
  &lt;/select&gt;
  
  &lt;select disabled&gt;
    &lt;option value="volvo"&gt;Volvo&lt;/option&gt;
    &lt;option value="saab"&gt;Saab&lt;/option&gt;
    &lt;option value="mercedes"&gt;Mercedes&lt;/option&gt;
    &lt;option value="audi"&gt;Audi&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>As you can see, my second select have the disabled attribute. I would like in javascript, when I selected the option <strong>"car"</strong> in my first select, the second select with the car's choice become enabled to make a choice.</p>
  
  <p>How can I proceed in javascript?</p>