Added Difficulty API.

By: EvilSeph <evilseph@gmail.com>

paper-api/src/main/java/org/bukkit/Server.java

@@ -323,18 +323,18 @@ public interface Server {
      * @return World with the given Unique ID, or null if none exists.
      */
     public World getWorld(UUID uid);
-    
+
     /**
      * Gets the map from the given item ID.
-     * 
+     *
      * @param id ID of the map to get.
      * @return The MapView if it exists, or null otherwise.
      */
     public MapView getMap(short id);
-    
+
     /**
      * Create a new map with an automatically assigned ID.
-     * 
+     *
      * @param world The world the map will belong to.
      * @return The MapView just created.
      */