bael-8622 getAndIncrement - fix based on email feedback

I believe there is a mistake in the code in Section 6 of the article
https://www.baeldung.com/java-atomicinteger-load-balancer

Specifically, the current code is:
public String getServer() {
    int index = counter.get() % serverList.size();
    counter.incrementAndGet();
    return serverList.get(index);
}

But I believe the correct code should be:
public String getServer() {
    int index = counter.getAndIncrement() % serverList.size();
    return serverList.get(index);
}

In the current code of the article, several threads could be calling
getServer() at the same time, execute counter.get() in sequence, all get
the same server number (index), before each incrementing the counter.
This would mean one server gets more uses, and other servers are
skipped, breaking a fair round-robin strategy.

Author: ulisseslima

core-java-modules/core-java-concurrency-advanced-6/src/main/java/com/baeldung/atomic/AtomicLoadBalancer.java

@@ -12,8 +12,7 @@ public AtomicLoadBalancer(List<String> serverList) {
     }
 
     public String getServer() {
-        int index = counter.get() % serverList.size();
-        counter.incrementAndGet();
+        int index = counter.getAndIncrement() % serverList.size();
         return serverList.get(index);
     }