Doc doesn't list `ws://` or `wss://` as valid URI schemes

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- [ x] Bug exists Release Version 1.2.0 ( Master Branch)
- [ x] Bug exists in MQTTv3 Client on Snapshot Version 1.2.1-SNAPSHOT (Develop Branch)
- [ x] Bug exists in MQTTv5 Client on Snapshot Version 1.2.1-SNAPSHOT (Develop Branch)

If this is a bug regarding the Android Service, please raise the bug here instead: https://github.com/eclipse/paho.mqtt.android/issues/new

The Javadoc still only lists `tcp://`, `ssl://` and `local://` as valid URI scheme even though websocket support has been added.

Also should probably allow `mqtt://` and `mqtts://` to the v5 branch as mentioned in #464

Raising this after poking around for the following Stack Overflow question: https://stackoverflow.com/questions/55519108/supported-protocol-with-node-mqtt-2-14-0-vs-org-eclipse-paho-client-mqttv3

Will try and remember to do a pull request to update this over the weekend if I get time, but don't let me stop anybody else jumping on it with a spare 5mins.