Reduce reliably on browser sniffing
Reduce reliably on browser sniffing

According to
https://groups.google.com/forum/#!msg/discuss-webrtc/OXqm0tjg8hs/hPA8azM
HFgAJ we can use `RTCPeerConnection.prototype.getStats.length === 0` to
detect the promise-based implementation of `getStats()` which
simplifies this code greatly!

jeregrine/simple-peer,feross/simple-peer