doc: update deno example

examples/with-deno/index.js

@@ -1,24 +1,14 @@
 /**
  * To run this example with Deno, run the following command:
  * deno run --allow-net --allow-read --allow-write index.js
+ *
+ * Note: Requires Deno versions greater than v1.39.0, which introduced the ImageData Web API
  */
 import { decode } from 'https://unpkg.com/@jsquash/jpeg@latest?module';
 import { encode } from 'https://unpkg.com/@jsquash/webp@latest?module';
 
-// Polyfill ImageData for Deno
-// Issue for tracking implementation: https://github.com/denoland/deno/issues/19288
-if (typeof ImageData === 'undefined') {
-  globalThis.ImageData = class ImageData {
-    constructor(data, width, height) {
-      this.data = data;
-      this.width = width;
-      this.height = height;
-    }
-  };
-}
-
-const pngBuffer = await Deno.readFile('example.jpg');
-const imageData = await decode(pngBuffer);
+const jpegBuffer = await Deno.readFile('example.jpg');
+const imageData = await decode(jpegBuffer);
 const webpBuffer = await encode(imageData);
 
 // Deno writeFile requires a Uint8Array as input