Update a url in framework.md (#33)

Author: zrmor

docs/apps/framework.md

@@ -84,7 +84,7 @@ $ mriqc /data/bids_root /data/bids_root/derivatives/ group
 ## What are *BIDS Derivatives*? 
 
 *NiPreps* generate *derivatives* of the original data, and they fulfill the BIDS specification for the results of Apps that are created for subsequent consumption by other BIDS-Apps.
-These derivatives must follow the BIDS Derivatives specification ([draft](https://bids-specification.readthedocs.io/en/derivatives/)).
+These derivatives must follow the BIDS Derivatives specification ([draft](https://bids-specification.readthedocs.io/en/stable/derivatives/introduction.html)).
 An example of BIDS Derivatives filesystem tree, generated with *fMRIPrep* 1.5:
 ```
 derivatives/
@@ -126,4 +126,4 @@ derivatives/
 [Singularity]: https://sylabs.io/singularity/
 [Docker]: https://docker.com
 [Docker Runtime]: https://www.docker.com/products/container-runtime
-[Docker Hub]: http://hub.docker.com
+[Docker Hub]: http://hub.docker.com