URLs in readme.md points to the old repo

[Kacper Aniołek]

The readme.md says to git clone https://github.com/alhoqbani/slim-php-realworld-example-app.git, then, the readme in cloned repository says the repository was moved ¯_(ツ)_/¯

I think it should be updated to point to https://github.com/gothinkster/slim-php-realworld-example-app.git

Edit: oh, it seems there are other links pointing to the old repo as well