Fix a typo in director-scene-layer-and-spirte.

Fix a typo in director-scene-layer-and-spirte of v2.

The "时间" in it should be "事件".

Also the link of Contributor Guide in READE.md is invalid now, so if there are only thing else I need to do before commit, please tell me.

修正了v2版本的导演、场景、层及精灵文档中的错别字。

文档中的“时间”应该是“事件”

另外README.md中的Contributor Guid链接失效了，如果此提交有任何问题请告诉我修正。