Decorator dependency is not compatible

[Fieldistor]

There is a new version of https://pypi.org/project/decorator/ (5.0) and it is not compatible with current version of the retry library. You have to add decorator==4.4.2 to make it work... Can we restrict the decorator dependency to <5.0.0?

[albertyw]

+1.

decorator v5 also requires python 3 to install (yes, I know we should update from python 2 to python 3)