Log the amount of local tracks properly

This changes a log message from “initialized with %s local tracks 2” to “initialized with 2 local tracks”.

conference.js

                         track.mute();
                     }
                 });
-                logger.log('initialized with %s local tracks', tracks.length);
+                logger.log(`initialized with ${tracks.length} local tracks`);
                 this._localTracksInitialized = true;
                 con.addEventListener(
                     JitsiConnectionEvents.CONNECTION_FAILED,