Update custom_render.html

Fixes mixed content error logging from the demo website over at jqueryui.com

Mixed Content: The page at '<URL>' was loaded over HTTPS, but requested an insecure element '<URL>'. This request was automatically upgraded to HTTPS, For more information see <URL>
VM25 jquery-3.6.0.js:6591 Mixed Content: The page at 'https://jqueryui.com/resources/demos/selectmenu/custom_render.html' was loaded over HTTPS, but requested an insecure element 'http://www.gravatar.com/avatar/b3e04a4…?d=monsterid&r=g&s=16'. This request was automatically upgraded to HTTPS, For more information see https://blog.chromium.org/2019/10/no-more-mixed-messages-about-https.html

Author: markvantilburg

demos/selectmenu/custom_render.html

@@ -113,9 +113,9 @@ <h2>Selectmenu with custom avatar 16x16 images as CSS background</h2>
 	<fieldset>
 		<label for="people">Select a Person:</label>
 		<select name="people" id="people">
-			<option value="1" data-class="avatar" data-style="background-image: url('http://www.gravatar.com/avatar/b3e04a46e85ad3e165d66f5d927eb609?d=monsterid&amp;r=g&amp;s=16');">John Resig</option>
-			<option value="2" data-class="avatar" data-style="background-image: url('http://www.gravatar.com/avatar/e42b1e5c7cfd2be0933e696e292a4d5f?d=monsterid&amp;r=g&amp;s=16');">Tauren Mills</option>
-			<option value="3" data-class="avatar" data-style="background-image: url('http://www.gravatar.com/avatar/bdeaec11dd663f26fa58ced0eb7facc8?d=monsterid&amp;r=g&amp;s=16');">Jane Doe</option>
+			<option value="1" data-class="avatar" data-style="background-image: url('https://www.gravatar.com/avatar/b3e04a46e85ad3e165d66f5d927eb609?d=monsterid&amp;r=g&amp;s=16');">John Resig</option>
+			<option value="2" data-class="avatar" data-style="background-image: url('https://www.gravatar.com/avatar/e42b1e5c7cfd2be0933e696e292a4d5f?d=monsterid&amp;r=g&amp;s=16');">Tauren Mills</option>
+			<option value="3" data-class="avatar" data-style="background-image: url('https://www.gravatar.com/avatar/bdeaec11dd663f26fa58ced0eb7facc8?d=monsterid&amp;r=g&amp;s=16');">Jane Doe</option>
 		</select>
 	</fieldset>
 </form>