Fix remaining Checkstyle errors for Singleton

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

@@ -41,7 +41,8 @@ public final class InitializingOnDemandHolderIdiom {
   /**
    * Private constructor.
    */
-  private InitializingOnDemandHolderIdiom() {}
+  private InitializingOnDemandHolderIdiom() {
+  }
 
   /**
    * Sigleton instance.

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

@@ -31,7 +31,8 @@ public final class IvoryTower {
   /**
    * Private constructor so nobody can instantiate the class.
    */
-  private IvoryTower() {}
+  private IvoryTower() {
+  }
 
   /**
    * Static to class instance of the class.