fix(server): echo the hostname rather than listenAddress (#3532)

The listenAddress is an IP level number, which may be "::" on IPV6.
The hostname is a string set in a /etc config file.
When these differ the hostname is clearer.

lib/server.js

@@ -177,7 +177,7 @@ class Server extends KarmaEventEmitter {
       }
 
       webServer.listen(this._boundServer, () => {
-        this.log.info(`Karma v${constant.VERSION} server started at ${config.protocol}//${config.listenAddress}:${config.port}${config.urlRoot}`)
+        this.log.info(`Karma v${constant.VERSION} server started at ${config.protocol}//${config.hostname}:${config.port}${config.urlRoot}`)
 
         this.emit('listening', config.port)
         if (config.browsers && config.browsers.length) {