- Linting (ESLint): Update polyfills to new compat rules of

eslint-config-ash-nazg and adhere to new rules (prefer `for-of`
  (or array methods) to `for`, catch preferred `includes` to `indexOf`);
  avoid `no-zero-fractions` rule for now
- npm: Update devDeps (removing one unneeded)

editor/external/dom-polyfill/dom-polyfill.js

@@ -108,7 +108,7 @@ const ChildNode = {
   },
   remove () {
     if (!this.parentNode) { return; }
-    this.parentNode.removeChild(this);
+    this.parentNode.removeChild(this); // eslint-disable-line unicorn/prefer-node-remove
   }
 };