Shape Trees specification link is broken

https://shapetrees.github.io/specification/spec possible moved to https://shapetrees.org/TR/specification/

Line 18 in d2d910b

    
           This specification uses the [TREE specification](https://treecg.github.io/specification) for its collection and fragmentation (or pagination) features, which in its turn is compatible to other specifications such as [[!activitystreams-core]], [[!VOCAB-DCAT-2]], [[!LDP]] or [Shape Trees](https://shapetrees.github.io/specification/spec). For the specific compatibility rules, read the [TREE specification](https://treecg.github.io/specification).

Now also the shapetrees.org domain name is down, but otherwise this link is the official one now which has been updated in the spec.