Changed documentation for RegainReason.REGEN ENUM to reflect latest code.

By: EvilSeph <evilseph@gmail.com>

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

@@ -60,7 +60,7 @@ public class EntityRegainHealthEvent extends EntityEvent implements Cancellable
     public enum RegainReason {
 
         /**
-         * When a player regains health from regenerating due to Peaceful mode (spawn-monsters=false)
+         * When a player regains health from regenerating due to Peaceful mode (difficulty=0)
          */
         REGEN,
         /**