Fix wombat.js include on pywb playback.

Pywb includes wombat.js to fix up URLs that are missed on the server-side. We have it in static/js, but pywb uses a different path. This fixes the path so it'll actually include properly.

DEPLOYMENT NOTES:
- run pip install -r requirements.txt to upgrade pywb to the latest version
- this requires changing the nginx config to add the /static/ route to user-content.perma.cc