Typo in the overall architecture

[DayuZhu]

Dubbo的开发文档中文版中的框架设计 整体设计图的 ExchangeSerever 是不是拼写错误？！

[ralf0131]

Yes, however it is difficult to fix it unless we have the raw file.

[beiwei30]

we do have raw file, let me fix it.

[justinmclean]

Hi,

we do have raw file, let me fix it.

Might be a good idea to check the raw file into version control if it not already? Thanks, Justin