NXDL source link to the bottom of each definitions' page is not adaptive

[mkuehbach]

There is a bug in our nx docs building: the NXDL source link to the bottom of each definitions' page is not adaptive.
It always points to the fairmat branch. While this is correct for deploying feature branches on fairmat, it is incorrect for local development as then the link should point to the respective file on ones own computer.