Change default for keepalive autodisconnect config

By default, automatically disconnect if no response. This is preferable
because we can sometimes lose connectivity without receiving a close
event from the socket, but it's also possible that the endpoint may not
support responses.

// FREEBIE

js/libtextsecure.js

@@ -38636,7 +38636,7 @@ TextSecureWebSocket = function (url, opts) {
             }
             this.disconnect = opts.disconnect;
             if (this.disconnect === undefined) {
-                this.disconnect = false;
+                this.disconnect = true;
             }
             this.wsr = websocketResource;
             this.reset();