footer.hbs: tweak scrollToTop. (#2465)
footer.hbs: tweak scrollToTop. (#2465)

* use `addEventListener`
* use `event.preventDefault()`
* remove unneeded parentheses
* remove `$` from the variable name
nodejs/new.nodejs.org,phillipj/new.nodejs.org,phillipj/new.nodejs.org,nodejs/new.nodejs.org