JS: Add placeholder in attribute to trap test

Author: asgerf

javascript/extractor/tests/generatedcode/input/test.html

@@ -10,5 +10,7 @@ <h1>{{title}}</h1>
       var data2 = {{ user_data2 | json | safe }};
       var data3 = <%- user_data3 %>;
     </script>
+    <a href="{{ attr1 }}" title="{{{ attr2 }}}" data-foo="<%- attr3 %>"
+       data-bar="   {{ attr4 }} "></a>
   </body>
 </html>