Fix typo in previous commit

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/event/world/PortalCreateEvent.java

@@ -74,7 +74,7 @@ public class PortalCreateEvent extends WorldEvent implements Cancellable {
          */
         FIRE,
         /**
-         * When a nether portal frame and portal is created at the exist of an
+         * When a nether portal frame and portal is created at the exit of an
          * entered nether portal.
          */
         NETHER_PAIR,