Fix missing Exception in setup.py
Fix missing Exception in setup.py

ModuleNotFoundError is unknown before python 3.6. It's use in doc_opts()
therefore causes trouble when sphinx is not installed for python versions
< 3.6.

EMS-TU-Ilmenau/fastmat,EMS-TU-Ilmenau/fastmat,EMS-TU-Ilmenau/fastmat