Simplify the code

[whyme0]

travel-expense-manager/backend/backend/core/managers.py

Lines 29 to 31 in 4d51991

	if extra_fields.get('is_staff') is not True:
	raise ValueError('Superuser must have is_staff=True.')
	if extra_fields.get('is_superuser') is not True:

Why it's not better to use False instead not True?

[vreaxe]

Thank you so much for your suggestion. I think you are right.
Feel free to make a pull request to change it.