Demo doesn't work on latest version

The demo doesn't run on the latest version of LÖVE, due to the sound API changing.

Since it's on another branch, I'm not sure how doing such a pull request would work but here is the commit I made so it runs: https://github.com/gabrc52/bump.lua-demo/commit/73a7d06ac654b5bfbdad1c25b99317959b57dd6d

