NEP29+1y: Drop Python 3.5

Author: effigies

setup.cfg

@@ -13,7 +13,6 @@ classifiers =
     License :: OSI Approved :: MIT License
     Operating System :: OS Independent
     Programming Language :: Python
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
@@ -28,7 +27,7 @@ provides =
     nisext
 
 [options]
-python_requires = >=3.5.1
+python_requires = >=3.6
 install_requires =
     numpy >=1.13
     packaging >=14.3