spring 源代码下载方法

spring的源代码地址发生了更改，以前的地址是 https://src.springframework.org/svn/spring-framework/。但现在spring的代码开始使用Git进行管理，新的源代码地址为：https://github.com/SpringSource/spring-framework。

因为 GitHub 同样支持svn的客户端，因而仍然可以使用svn的命令进行代码checkout。

附官方解释：

The Spring Framework repository has moved to http://github.com/SpringSource/spring-framework.

See the readme there for details on working with Git, building the framework, etc.

Note that svn-based access is still available via GitHub's support for Subversion clients, e.g.:

    $ svn checkout https://github.com/SpringSource/spring-framework

See https://github.com/blog/966-improved-subversion-client-support for more details.