Update setup.py with dependency ranges
Update setup.py with dependency ranges

- Updates setup.py to remove locks to minor/patch versions of the dependencies
- Replaces locked dependencies with dependency ranges

Closes #1538 

cc/ @BertR @rkdarst
jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jhamrick/nbgrader