Added Sky biome for the Skylands. Thanks robin0van0der0v!

src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java

@@ -356,6 +356,8 @@ public class CraftBlock implements Block {
             return Biome.TUNDRA;
         } else if (base == BiomeBase.HELL) {
             return Biome.HELL;
+        } else if (base == BiomeBase.SKY) {
+            return Biome.SKY;
         }
 
         return null;