tour: [Binary version] Link broken on tour/basics/4

Context: http://127.0.0.1:3999/tour/basics/4

On section:
(For more about why types look the way they do, see the [article on Go's declaration syntax](http://127.0.0.1:3999/blog/gos-declaration-syntax).)

The link is broken, we need a link to fixed blog host (maybe go.dev) 