removed extra "is" from the javadoc of InitializingOnDemandHolderIdiom class

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

@@ -26,7 +26,7 @@ package com.iluwatar.singleton;
  * The Initialize-on-demand-holder idiom is a secure way of creating a lazy initialized singleton
  * object in Java.
  * <p>
- * The technique is is as lazy as possible and works in all known versions of Java. It takes advantage
+ * The technique is as lazy as possible and works in all known versions of Java. It takes advantage
  * of language guarantees about class initialization, and will therefore work correctly in all
  * Java-compliant compilers and virtual machines.
  * <p>