Missing PSR-4 reference in PSR-1

When I created the [Amendment bylaw](https://github.com/php-fig/fig-standards/blob/master/bylaws/006-psr-amendments.md) I [added a PSR-4 reference into PSR-1](https://github.com/php-fig/fig-standards/commit/0da2fc792762b33d56f70d2efe7c7c1c0d4f3e07) as part of the package, and that was all approved and voted on and good in the group.

It seems like I forgot to add a PSR-4 reference into the second "PSR-0 only" reference. This was a foolish mistake, so this PR seeks to correct that.