docs: update catalog links in v1beta1 migration doc 📖
docs: update catalog links in v1beta1 migration doc 📖

Those were pointing to the now "deprecated" v1beta1 branch. Pointing
to the master branch and the correct folder now.

Signed-off-by: Vincent Demeester <b98c0fd48a8945096c766de790fe70420dd2f223@redhat.com>

tektoncd/pipeline,tektoncd/pipeline