fix(example): add missing dependency howler

[ju1m]

Needed to avoid:

$ npm run esbuild -- --serve=9000 --servedir=public

> esbuild
> esbuild app.ts public/submodules/codebase-ui/src/unisonShare.js public/submodules/seeds-game/src/index.ts --bundle --outdir=public/build --public-path=/build/ --loader:.svg=file --loader:.woff2=file --loader:.mp3=file --serve=9000 --servedir=public


 > Local:   http://127.0.0.1:9000/
 > Network: http://192.168.4.100:9000/
 > Network: http://10.0.0.10:9000/
 > Network: http://172.16.0.1:9000/

✘ [ERROR] Could not resolve "pepjs"

    public/submodules/seeds-game/src/index.ts:2:7:
      2 │ import "pepjs";
        ╵        ~~~~~~~

  You can mark the path "pepjs" as external to exclude it from the bundle, which
  will remove this error and leave the unresolved path in the bundle.

✘ [ERROR] Could not resolve "howler"

    public/submodules/seeds-game/src/ts/audio.ts:1:21:
      1 │ import { Howl } from "howler";
        ╵                      ~~~~~~~~

  You can mark the path "howler" as external to exclude it from the bundle, which
  will remove this error and leave the unresolved path in the bundle.

2 errors