Run GreenThumbTimer on the current tick

It avoids onBlockBreak to be called twice (which basically launched
the task twice). I don't know what were the consequences but that
wasn't right anyway.
Also it would be better if we wouldn't have to cancel the event,
because there is a possibility that plugins like LogBlock don't have a
chance to process it.

src/main/java/com/gmail/nossr50/skills/herbalism/Herbalism.java

@@ -289,7 +289,7 @@ public class Herbalism {
                 break;
             }
 
-            plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new GreenThumbTimer(block, profile, type), 1);
+            plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new GreenThumbTimer(block, profile, type), 0);
             player.updateInventory();   // Needed until replacement available
         }
     }