Changed TimeSource subscription to use topic /clock.

Fix #696

Author: wayneparrott

lib/time_source.js

@@ -22,7 +22,7 @@ const { Parameter, ParameterType } = require('./parameter.js');
 const Time = require('./time.js');
 
 const USE_SIM_TIME_PARAM = 'use_sim_time';
-const CLOCK_TOPIC = 'clock';
+const CLOCK_TOPIC = '/clock';
 
 /**
  * @class - Class representing a TimeSource in ROS

test/test-time-source.js

@@ -51,7 +51,7 @@ describe('rclnodejs TimeSource testing', function() {
   });
 
   function publishClockMessage(node) {
-    let pub = node.createPublisher('builtin_interfaces/msg/Time', 'clock');
+    let pub = node.createPublisher('builtin_interfaces/msg/Time', '/clock');
     let count = 0;
     timer = setInterval(() => {
       pub.publish({ sec: count, nanosec: 0 });