require python 3.5+ (#26330)

Author: TomAugspurger

setup.py

@@ -781,5 +781,5 @@ def srcpath(name=None, suffix='.pyx', subdir='src'):
       long_description=LONG_DESCRIPTION,
       classifiers=CLASSIFIERS,
       platforms='any',
-      python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*',
+      python_requires='>=3.5',
       **setuptools_kwargs)