Add stricter/better ESLint config (#589)

* Add stricter/better ESLint config

* Remove more unnecessary @returns

src/util/Collection.js

@@ -47,7 +47,7 @@ class Collection extends Map {
   /**
    * If the items in this collection have a delete method (e.g. messages), invoke
    * the delete method. Returns an array of promises
-   * @return {Array<Promise>}
+   * @returns {Array<Promise>}
    */
   deleteAll() {
     const returns = [];