Remove outdated mention of --no-symlink
Remove outdated mention of --no-symlink

dementrock/nbgrader,ellisonbg/nbgrader,jupyter/nbgrader,modulexcite/nbgrader,jupyter/nbgrader,MatKallada/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,ellisonbg/nbgrader,jhamrick/nbgrader,dementrock/nbgrader,EdwardJKim/nbgrader,EdwardJKim/nbgrader,MatKallada/nbgrader,EdwardJKim/nbgrader,alope107/nbgrader,jhamrick/nbgrader,alope107/nbgrader,jhamrick/nbgrader,modulexcite/nbgrader,ellisonbg/nbgrader,jupyter/nbgrader,jupyter/nbgrader,ellisonbg/nbgrader,EdwardJKim/nbgrader