Remove upper bound to celery dependency

[Viicos]

Considering the usage of Celery in the library (only shared_task), I don't think adding an upper bound is necessary.

[sastred]

Hi Viicos,

I agree that the usage is very small but I prefer to minimize possible breaking changes in Celery. I think we can change the dependency to 'celery>=5.0,<6'. Do you agree?

[Viicos]

I agree that the usage is very small but I prefer to minimize possible breaking changes in Celery. I think we can change the dependency to 'celery>=5.0,<6'. Do you agree?

If it was me I would rather go with no upper bounds (I usually like to link this article) but I'm fine with <6!

[sastred]

Thanks for the link, it's very interesting and it has very good points. However, I think of Celery more as a queue framework rather than a small library. Reviewing the v4 -> v5 changelog there are a couple of sentences that suggest that it is not safe to upgrade to major versions automatically:

Starting from now users should expect more frequent releases of major versions as we move fast and break things to bring you even better experience.

Celery 5.0 introduces a new CLI implementation which isn’t completely backwards compatible.

I prefer to set a <6 dependency and check if it keeps working when 6.0 is released.

[coveralls]

coverage: 76.864%. remained the same
when pulling 3e7b909 on Viicos:celery-version
into 8a356ec on APSL:master.