Made NamedTuple final

Author: rp-bg

src/main/java/com/appxiom/ax/tuple/NamedTuple.java

@@ -14,7 +14,7 @@
 /**
  * Represents a tuple where each element is associated with a specific name
  */
-public class NamedTuple {
+public final class NamedTuple {
 
     /**
      * The internal map storing the named elements of the tuple.