Fix jumping time in beets.js

[waweic]

Round was used instead of floor, so the minute counter jumped after each 30 seconds

[sampsyo]

Awesome; thank you. That was a dumb mistake. Would you mind adding a quick changelog entry about the fix?

[waweic]

You are welcome, of course. I have never contributed to a changelog before and don't really know how to write an entry. How would you formulate that?

[sampsyo]

Sure! Just add a bullet to the end of the current "Fixes" list at the top of changelog.rst saying, for example:

* :doc:`/plugins/web`: The time display in the web interface would incorrectly jump
  at the 30-second mark of every minute. Now, it correctly changes over at zero
  seconds. :bug:`2822`

[waweic]

Thanks! If you don't mind, I will just take this for the changelog entry.

[sampsyo]

Looks great; thank you! ✨