feat(morris): transparent morris.js background

src/app/pages/charts/morris/morris.module.js

@@ -7,6 +7,7 @@
 
   angular.module('BlurAdmin.pages.charts.morris', [])
     .config(routeConfig).config(function(){
+      Morris.Donut.prototype.defaults.backgroundColor = 'transparent';
       Morris.Donut.prototype.defaults.labelColor = 'rgba(255,255,255,0.8)';
       Morris.Grid.prototype.gridDefaults.gridLineColor = 'rgba(255,255,255,0.8)';
       Morris.Grid.prototype.gridDefaults.gridTextColor = 'rgba(255,255,255,0.8)';