fix: update latching check and test

Author: Dimitri Nikitopoulos

src/lib/RosNode.js

@@ -115,7 +115,7 @@ class RosNode extends EventEmitter {
     if (!subImpl) {
       subImpl = new SubscriberImpl(options, this);
       this._subscribers[topic] = subImpl;
-      this.firstSubscriber = true;
+      firstSubscriber = true;
     }
 
     const sub = new Subscriber(subImpl);

test/xmlrpcTest.js

@@ -740,7 +740,7 @@ describe('Protocol Test', () => {
       });
     });
 
-    it.only('2 Subscribers on Same Latched Topic subscribing at different times ', function(done) {
+    it('2 Subscribers on Same Latched Topic subscribing at different times ', function(done) {
       this.slow(1000);
       const nh = rosnodejs.nh;