Add tox to test-requirements
Add tox to test-requirements

mgkwill/spectrometer,zxiiro/spectrometer,dave-tucker/spectrometer,zxiiro/spectrometer,mgkwill/spectrometer,mgkwill/spectrometer,dave-tucker/spectrometer,dave-tucker/spectrometer,mgkwill/spectrometer,zxiiro/spectrometer,mgkwill/spectrometer,dave-tucker/spectrometer,zxiiro/spectrometer,zxiiro/spectrometer,dave-tucker/spectrometer