- Linting (ESLint): Replace innerHTML with textContent from old demo

- npm: Update devDeps (including core-js copy)

screencasts/svgopen2010/script.js

@@ -93,7 +93,7 @@ Slide.prototype = {
   _makeCounter () {
     if (!this._count || !this._node) { return; }
     const c = doc.createElement('span');
-    c.innerHTML = this._count;
+    c.textContent = this._count;
     c.className = 'counter';
     this._node.append(c);
   },