The Zend Framework blog has a post announcing the name change of the main Zend Framework repository on GitHub:
Per the GitHub documentation on renames, existing links will be automatically redirected, and will persist as long as we do not create a new repository with the name "zf2". Redirects occur for: issues, wikis, stars, followers and git operations.
The post also includes the instructions on how to update your current "remotes" in your git checkout (so you don't have to re-clone). It also mentions the change and how it relates to Composer - hint: nothing at all because of how Composer works.