fix: relayed webrtc passes circuit matcher

[SgtPooki]

fixes #36

I'm not sure if it's intentional that relayed webrtc multiaddrs are not passing Circuit.matches tests

[achingbrain]

This module has two types of matching - .matches and .exactMatch

An address that .matches can have additional path components that might make it .matches other address types. .exactMatch means the address is unequivocally of that type.

E.g.:

const address = multiaddr('/dns/example.com/tcp/80/ws')

TCP.matches(address) // true, starts with a TCP address
TCP.exactMatch(address) // false is a WebSocket address

By adding the literal('webrtc') component, it will make Circuit.exactMatch return true for WebRTC addresses which would be a bug.

What you could do is make the peerId() optional:

const _Circuit = and(_P2P, literal('p2p-circuit'), optional(peerId()))

...but then you wouldn't actually have a valid circuit relay address since you need the final peer id to tell the relay which peer you're trying to reach.