Fix terminal carousel on landing page of docs

This isn't perfect, but it is a step in the right direction. This fixes
the prev button not working at all and the next button having some
undesirable behavior.

This seems to work for the most part, but I noticed that if I leave this
open and go to a different tab in my browser, there's some strange
behavior when I come back to the landing page: there are multiple
outputs playing at once. This is similar to the current behavior, where
clicking the next button multiple times does the same thing.