Small tweak to download glyphicon

ui/arena/index.html

@@ -37,7 +37,9 @@
                 <div id="fetch-area">
                     <label for="fetch-url">Source URI:</label>
                     <div class="input-group">
-                        <span class="input-group-addon">@</span>
+                        <span class="input-group-addon">
+                            <span class="glyphicon glyphicon-cloud-download"></span>
+                        </span>
                         <input type="url" class="form-control" id="fetch-url" placeholder="https://gist.github.com/...">
                         <span class="input-group-btn">
                             <button id="fetch-button" class="btn btn-default" type="button">fetch</button>