Corrected the adress of angular-seed in README.md

The angular-seed project hyperlink was pointing to the angularfire-seed github page. I replace the link older link ("https://github.com/angular/angularfire-seed") with "https://github.com/angular/angular-seed"
Merge pull request #60 from belgac/patch-1

Corrected the adress of angular-seed in README.md