logo: svg -> png

public/app/plugins/panel/piechart/plugin.json

@@ -11,8 +11,8 @@
       "url": "https://grafana.com"
     },
     "logos": {
-      "small": "img/piechart_logo_small.svg",
-      "large": "img/piechart_logo_large.svg"
+      "small": "img/piechart_logo_small.png",
+      "large": "img/piechart_logo_large.png"
     }
   }
 }