Added onStructureGrow event, thanks to md-5.

By: Nathan Adams <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/plugin/java/JavaPluginLoader.java

@@ -677,6 +677,12 @@ public class JavaPluginLoader implements PluginLoader {
                     ((WorldListener) listener).onPortalCreate((PortalCreateEvent) event);
                 }
             };
+        case STRUCTURE_GROW:
+            return new EventExecutor() {
+                public void execute(Listener listener, Event event) {
+                    ((WorldListener) listener).onStructureGrow((StructureGrowEvent) event);
+                }
+            };
 
         // Painting Events
         case PAINTING_PLACE: