simple-peer entry is a bit outdated

[corwin-of-amber]

I had no problems with webrtc-swarm using simple-peer@6.4.4 on Chrome, but on Safari it broke because that version was using the old (Promise-less) version of WebRTC.

Manually upgrading to simple-peer@9.4.0 solved the issue. So a simple change in package.json can save a lot of confusion for everyone.