Support decode message from Buffer object

[progre]

This is PR to fix Kurento/bugtracker#116 .
It makes decoding message from Buffer object. It depends on the behavior is changed by version up of websocket-stream.

To use in Kurento-client-js, It should be merged at the same time;
KurentoForks/reconnect-ws#1

[agonza1]

I tried both changes at the same time, the decoding seems to work fine but there is an unexpected behavior.
In some situations more than one JSON is sent to Kurento at the same time like:

kurento_1 | 0:00:12.528481475 1 0x7f8a7c0e9a40 DEBUG KurentoWebSocketTransport WebSocketTransport.cpp:427:processMessage: Message: {"jsonrpc":"2.0","method":"subscribe","params":{"object":"717845a1-027a-4eec-968f-485b8b1a8f86_kurento.MediaPipeline/e46d8a73-c325-4e0e-9aaf-4460d4ae6f1d_kurento.WebRtcEndpoint","type":"MediaStateChanged","sessionId":"16da30ec-249f-4c2a-80ea-32105fc3b676"},"id":30}{"jsonrpc":"2.0","method":"invoke","params":{"object":"717845a1-027a-4eec-968f-485b8b1a8f86_kurento.MediaPipeline/17fa6614-517e-499a-826e-645ff88a081f_kurento.WebRtcEndpoint","operation":"connect","operationParams":{"sink":"717845a1-027a-4eec-968f-485b8b1a8f86_kurento.MediaPipeline/e46d8a73-c325-4e0e-9aaf-4460d4ae6f1d_kurento.WebRtcEndpoint"},"sessionId":"16da30ec-249f-4c2a-80ea-32105fc3b676"},"id":31}

Kurento then grabs the first JSON object and leaves the rest out causing a timeout error.
I haven't discovered yet why this happens.

[jenkinskurento]

Hi there, thanks for your Pull Request!

A Kurento member needs to verify that this patch is reasonable to test. In case it is, they should write a comment with the phrase test this please. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by Kurento members will still work. Regular contributors can be whitelisted to skip this step.

[agonza1]

Update:
I had this consistently working with this changes of kurento-jsonrpc-js and this progre/reconnect-ws#1

Also npm audit of kurento-client-js returns 0 vulnerabilities