pom.xml: Update to kurento-client 6.18.0-SNAPSHOT
pom.xml: Update to kurento-client 6.18.0-SNAPSHOT

Open up access to the new API methods that get introduced in the Kurento
Java client 6.18 development version.

OpenVidu/openvidu,OpenVidu/openvidu,OpenVidu/openvidu,OpenVidu/openvidu,OpenVidu/openvidu,OpenVidu/openvidu