offlineimap is python2 only which is deprecated

[olaf7]

offlineimap is no longer actively developed and plans for python3 support are stalled. pyhton2 is depricated.

see:

• https://github.com/OfflineIMAP/offlineimap/issues/597] (1st comment by maintainer)
• [(https://www.python.org/doc/sunset-python-2/)]

[olaf7]

related to issue #56