pymel.util.enum: change cmp to stop hiding an error
pymel.util.enum: change cmp to stop hiding an error

previously, running the full unittest suite with pytest would fail the doctest for pymel.util.enum... but not if JUST the "pymel_test_output.bat pymel/util/enum.py" was run. Now at least it always fails...

assumptionsoup/pymel,assumptionsoup/pymel,david-lassonde-adsk/pymel,david-lassonde-adsk/pymel