Code style improvements in JavaScript (#13159)

* JS-linter: fix trailing comma's

* Configure eslinter to ignore this onchange error.

app/javascript/mastodon/components/intersection_observer_article.js

@@ -44,7 +44,7 @@ export default class IntersectionObserverArticle extends React.Component {
     intersectionObserverWrapper.observe(
       id,
       this.node,
-      this.handleIntersection
+      this.handleIntersection,
     );
 
     this.componentMounted = true;