Added RegainReason.ENDER_CRYSTAL.

By: EvilSeph <evilseph@gmail.com>

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

@@ -83,6 +83,10 @@ public class EntityRegainHealthEvent extends EntityEvent implements Cancellable
          * When a player regains health from eating consumables
          */
         EATING,
+        /**
+         * When an ender dragon regains health from an ender crystal
+         */
+        ENDER_CRYSTAL,
         /**
          * When a player is healed by a potion or spell
          */