fix: change rollup config so that npm run watch works

[squarebracket]

Description

I was annoyed with npm run watch not working properly, so I decided to try to fix it. I don't know if this is the right approach, but I did what video.js is doing with adding modules into the external config key.

With this + videojs/video.js#5966, you can change a file in VHS and it will be compiled into video.js. It takes a bit to compile, but I found that I would sometimes get some weird behaviour if I was loading both video.js and videojs-http-streaming.js.

Specific Changes proposed

Added the modules that caused compilation failure to the external config key for CommonJS and ES output.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[brandonocasey]

Going to give this a quick test, but I think this is the correct approach

EDIT: It works!