Fixed players being stuck in SPECTATOR after going through End Portal

Fixes #377

It was due to the SafeSpotTeleport not being flagged as "portal" when issuing the teleportation Nether -> End.

src/main/java/world/bentobox/bentobox/listeners/NetherPortals.java

@@ -128,6 +128,7 @@ public class NetherPortals implements Listener {
             new SafeSpotTeleport.Builder(plugin)
             .entity(e.getPlayer())
             .location(to)
+            .portal()
             .build();
         }
     }