Remove oversized images from generation

This should reduce tarball size and generation time.
Fixes #285

Author: dannystaple

src/fetch_image.js

@@ -1,7 +1,7 @@
 const Image = require("@11ty/eleventy-img");
 module.exports = async function (src) {
     return await Image(src, {
-        widths: [null, 300, 720, 940, 1200],
+        widths: [300, 720, 940],
         formats: ["jpeg", "png"],
         urlPath: "/assets/images/",
         outputDir: "./_site/assets/images/"