[pygobject] setup.py: add python_requires

[Christoph Reiter <creiter src gnome org>]

commit f2d8ca6e301d7daf14b984a28d93db3b9224277c
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Sun Jun 16 16:35:00 2019 +0200

    setup.py: add python_requires
    
    It gets used by pip>=9 to decide which version from pypi to install. Which means we can
    more easily drop older Python versions without having to worry about breaking anyones setup.
    
    Sadly our oldest supported system, Ubuntu Xenial, only has pip 8, so it will install
    the newest version and fail anyway if we drop Python 3.5 support. We can at least
    point users to update their pip in their virtual environments then.
    
    https://packaging.python.org/guides/distributing-packages-using-setuptools/#python-requires

 setup.py | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/setup.py b/setup.py
index 4ce87ef9..802594ec 100755
--- a/setup.py
+++ b/setup.py
@@ -1272,6 +1272,8 @@ def main():
             "install_pkgconfig": install_pkgconfig,
         },
         install_requires=install_requires,
+        python_requires=(
+            '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, <4'),
         data_files=[
             ('include/pygobject-3.0', ['gi/pygobject.h']),
         ],