Make Interval class final

The class is declared immutable. Users of this class can assume true
immutability when subclasses are not allowed.

Signed-off-by: Piotr Findeisen <[email protected]>

Author: findepi

runtime/Java/src/org/antlr/v4/runtime/misc/Interval.java

@@ -6,7 +6,7 @@
 package org.antlr.v4.runtime.misc;
 
 /** An immutable inclusive interval a..b */
-public class Interval {
+public final class Interval {
 	public static final Interval INVALID = new Interval(-1,-2);
 
 	public final int a;