Replace old requires-python with python-requires

requires-python is old value and does not work, python-requires
is right metadata.

'python-requires' is introduced from PEP440 and requires-python was old value
in PEP345.
- https://packaging.python.org/guides/distributing-packages-using-setuptools/#python-requires
- https://www.python.org/dev/peps/pep-0345/#requires-python

Change-Id: I6a28757f4a0bf5d47214f4ed548cf5c73d302e3f
1 file changed