Fix checkstyle error

singleton/src/main/java/com/iluwatar/singleton/ThreadSafeLazyLoadedIvoryTower.java

@@ -42,7 +42,7 @@ public final class ThreadSafeLazyLoadedIvoryTower {
   }
 
   /**
-   * The instance doesn't get created until the method is called for the first time
+   * The instance doesn't get created until the method is called for the first time.
    */
   public static synchronized ThreadSafeLazyLoadedIvoryTower getInstance() {
     if (instance == null) {