build: update prerequisites on progress towards Python 3
As recommended at https://github.com/nodejs/node/pull/25759#issuecomment-458139766
- Python 2.6 end of life statement in 2013: https://www.python.org/dev/peps/pep-0361/#release-lifespan
- Python 2.7 end of life statement in 2019: https://www.python.org/dev/peps/pep-0373/#update
- Python 3.4 reaches it end of life in < 50 days so it should not be a target: https://devguide.python.org/#branchstatus
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines