Use a loop to copy png image data instead of Buffer.copy

lib/image/png.js

@@ -118,9 +118,9 @@ class PNGImage {
       let i = p = a = 0;
       const len = pixels.length;
       while (i < len) {
-        pixels.copy(imgData, p, i, i + colorCount);
-        p += colorCount;
-        i += colorCount;
+        for (let colorIndex = 0; colorIndex < colorCount; colorIndex++) {
+          imgData[p++] = pixels[i++];
+        }
         alphaChannel[a++] = pixels[i++];
       }