added element id usage cost for download

yuyu/admin/projects_invoice/templates/projects_invoice/cost_tables.html

@@ -18,6 +18,7 @@
 
         <br/>
         <br/>
+        <div id="usage_cost">
         <div>
             <dl class="dl-horizontal">
                 <dt>Invoice Month</dt>
@@ -54,6 +55,7 @@
         <div id="image-cost">
             {{ image_cost_table.render }}
         </div>
+        </div>
     {% else %}
         <h1>Billing not enabled or you don't have any usage yet</h1> <br/>
     {% endif %}
@@ -71,6 +73,7 @@
         }
 
         function downloadPdf() {
+            console.log("CALLING DOWNLOAD")
             let opt = {
                 filename: 'usage_cost.pdf',
                 margin: [16, 16],