Replace documentation reference to outdated test environment py27-nonhdfs (#2762)
Replace documentation reference to outdated test environment py27-nonhdfs (#2762)

* Replace reference to outdated test environment py27-nonhdfs.

adaitche/luigi,PeteW/luigi,spotify/luigi,adaitche/luigi,spotify/luigi,jamesmcm/luigi,riga/luigi,riga/luigi,jamesmcm/luigi,adaitche/luigi,riga/luigi,PeteW/luigi,riga/luigi,dlstadther/luigi,spotify/luigi,adaitche/luigi,dlstadther/luigi,dlstadther/luigi,jamesmcm/luigi,jamesmcm/luigi,spotify/luigi,PeteW/luigi,PeteW/luigi,dlstadther/luigi