Fixes in initialize-canvas.js. Updated tests

audiogram/initialize-canvas.js

     Canvas = require("canvas"),
     getRenderer = require("../renderer/");
 
+const { Image } = require("canvas");
+
 function initializeCanvas(theme, cb) {
 
   // Fonts pre-registered in bin/worker
       return cb(err);
     }
 
-    const canvas = Canvas.createCanvas();
-    var bg = canvas.Image;
+    const bg = new Image();
     bg.src = raw;
+    
     renderer.backgroundImage(bg);
 
     return cb(null, renderer);

test/frame-test.js

     initializeCanvas = require("../audiogram/initialize-canvas.js"),
     drawFrames = require("../audiogram/draw-frames.js");
 
+const { Image } = require("canvas");
+
 require("mkdirp").sync(path.join(__dirname, "tmp", "frames"));
 
 var frameDir = path.join(__dirname, "tmp", "frames");
 
       test.error(e);
 
-      const canvas = Canvas.createCanvas();
-      var img = canvas.Image;
+      const img = new Image();
       img.src = f1;
 
       var bg = getColor(options.backgroundColor || "#fff"),