fixed stack link

app/templates/show_books.html

@@ -61,10 +61,7 @@
       <td>
         {% for stack in book.stacks %}
 
-              <li><a href="{{url_for('show_stack_by_id', id=stack.id)}}">  </a>
+              <li><a href="{{url_for('show_stack_by_id', id=stack.id)}}"> {{ stack.stack_name }} </a></li>
-
-                {{ stack.stack_name }} 
-                  </li>
 
       {% endfor %}