Add pale oak tree variants (#3087)

Author: SirYwell

worldedit-core/src/main/java/com/sk89q/worldedit/util/TreeGenerator.java

@@ -168,6 +168,8 @@ public boolean canGenerateOn(BlockType type) {
         MANGROVE("Mangrove tree", "mangrove"),
         TALL_MANGROVE("Tall mangrove tree", "tall_mangrove"),
         CHERRY("Cherry blossom", "cherry"),
+        PALE_OAK("Pale oak tree", "pale_oak"),
+        PALE_OAK_CREAKING("Pale oak creaking tree", "pale_oak_creaking"),
         RANDOM("Random tree", "rand", "random") {
             @Override
             public boolean generate(EditSession editSession, BlockVector3 pos) throws MaxChangedBlocksException {