net/mosquitto: Bump to version 1.3.4

A minor point release.

* Don’t ask client for certificate when require_certificate is false.
* Fix incorrect handling of anonymous bridges on the local broker.
* backout incomplete functionality incorrectly added in 1.3.2

Signed-off-by: Karl Palsson <karlp@remake.is>
net/mosquitto: update readme with protocol versions

Mosquitto has supported v3.1.1 of the mqtt protocol since verson 1.3

Signed-off-by: Karl Palsson <karlp@remake.is>