minor plugin fixes

app/views/plugins/templates/chart.html

@@ -11,7 +11,7 @@
 </head>
 <body>
   <div id="chart-container">
-    <img alt="Ajax loader" src="/assets/ajax-loader.gif" style="position: absolute; margin: auto; top: 0; left: 0; right: 0; bottom: 0;" />
+    <img alt="Ajax loader" src="//thingspeak.com/assets/ajax-loader.gif" style="position: absolute; margin: auto; top: 0; left: 0; right: 0; bottom: 0;" />
   </div>
 </body>
 </html>