Update top-level __init__.py
Update top-level __init__.py

The minimum versions that I set were somewhat arbitrary.  There is
also a mismatch in roman 2.0.0, for which roman.__version__ == '1.4'.
For the time being I guess we can just say that the minimum version of
roman is '1.4', though I wonder if this upstream problem may cause
minor headaches later.

StanczakDominik/PlasmaPy