Support for celery 5.0

[kirankumbhar]

Hello!
Jobtastic doesn't support celery 5.0. I tried with celery 5.0 and received the following error.

Python = 3.8.5
Celery = 5.0.0

"/Users/scorpionk/.virtualenvs/testenv/lib/python3.8/site-packages/testproj/testapp/tasks.py", line 6, in <module>
    from jobtastic import JobtasticTask
  File "/Users/scorpionk/.virtualenvs/testenv/lib/python3.8/site-packages/jobtastic/__init__.py", line 17, in <module>
    from jobtastic.task import JobtasticTask  # NOQA
  File "/Users/scorpionk/.virtualenvs/testenv/lib/python3.8/site-packages/jobtastic/task.py", line 24, in <module>
    from celery.task import Task
ModuleNotFoundError: No module named 'celery.task'