Log Message:
py-django-js-asset: updated to 1.2.1

1.2:
Reformatted the code using Black.
Added equality of JS() objects to avoid adding the same script more than once in \ 
the same configuration.
Determine the static callable at module import time, not each time a static path \ 
is generated.
Customized the repr() of JS() objects.
Added Python 3.7 and Django 2.2 to the test matrix.