need to update the checksum in the cell; it will be later corrected by overwritecells.preprocess_cell back to the original value
need to update the checksum in the cell; it will be later corrected by overwritecells.preprocess_cell back to the original value

jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jhamrick/nbgrader,jupyter/nbgrader