fix properties elementName;I checked the name used by Tile from 0.8.0 at least

I found cocos2d has same bug in all release versions.
the patch line is about around line 561.
and because I use VIM , it trims spaces automatically.

patch code:
-    } 
-    else if (elementName == "property")
+    }
+    else if (elementName == "properties")