Revert "Include pygments in docs requirements"
Revert "Include pygments in docs requirements"

This reverts commit 513658149bc27611fc77d3d91cbcf8f73eef5450.

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