Added DamageCause.SUICIDE.

By: EvilSeph <evilseph@gmail.com>

paper-api/src/main/java/org/bukkit/event/entity/EntityDamageEvent.java

@@ -143,6 +143,12 @@ public class EntityDamageEvent extends EntityEvent implements Cancellable {
          * Damage: 5
          */
         LIGHTNING,
+        /**
+         * Damage caused by committing suicide using the command "/kill"
+         *
+         * Damage: 1000
+         */
+        SUICIDE,
         /**
          * Custom damage.
          *