Change access level to private

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

@@ -53,7 +53,7 @@ public final class InitializingOnDemandHolderIdiom {
    * Provides the lazy-loaded Singleton instance.
    */
   private static class HelperHolder {
-    public static final InitializingOnDemandHolderIdiom INSTANCE =
+    private static final InitializingOnDemandHolderIdiom INSTANCE =
         new InitializingOnDemandHolderIdiom();
   }
 }