gunits @2.18.1: requires module python_requests to match python used

[kencu (Ken)]

when first instaling or when trying to update currencies with gunit_cur, this error occurs:

Trying to update currency.units (will use existing file if this fails)
./units_cur currency.units
Traceback (most recent call last):
  File "./units_cur", line 57, in <module>
    import requests
ImportError: No module named requests

it can be solved by requiring the python_requests module to match the python version being used (currently random, see 58780 )