Merge pull request #8737 from twbs/docs-html5-style-select-multiple

CSS docs page: Use simpler HTML5 style for `multiple` <select> attribute

css.html

@@ -1425,7 +1425,7 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
 {% endhighlight %}
 
     <h3>Selects</h3>
-    <p>Use the default option or specify a <code>multiple="multiple"</code> to show multiple options at once.</p>
+    <p>Use the default option, or add <code>multiple</code> to show multiple options at once.</p>
     <form class="bs-example">
       <select class="form-control">
         <option>1</option>
@@ -1435,7 +1435,7 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
         <option>5</option>
       </select>
       <br>
-      <select multiple="multiple" class="form-control">
+      <select multiple class="form-control">
         <option>1</option>
         <option>2</option>
         <option>3</option>