Adjust checkstyle rules. Make checkstyle fail the build when violations are found. Correct all current checkstyle violations.

double-checked-locking/src/test/java/com/iluwatar/doublechecked/locking/InventoryTest.java

@@ -77,8 +77,8 @@ public class InventoryTest {
     final ExecutorService executorService = Executors.newFixedThreadPool(THREAD_COUNT);
     for (int i = 0; i < THREAD_COUNT; i++) {
       executorService.execute(() -> {
-        while (inventory.addItem(new Item())) ;
-      });
+          while (inventory.addItem(new Item())) {};
+        });
     }
 
     // Wait until all threads have finished