Circular dependency on relativetimebuilder

[Former user]

There is a circular dependency in install_requires:

aniso8601 requires relativetimebuilder>=0.2.0 relativetimebuilder requires aniso8601>=5.0.0

One or the other should be excluded.

[Brandon Nielsen]

Fixed in aniso8601 6.0.0 / relativetimebuilder 1.0.0.