setup: Increase required setuptools version

This is required for installing namespace packages from wheels
build with newer versions of setuptools (see setuptools issue 885)

Fixes gh-2600

Author: ales-erjavec

requirements-core.txt

@@ -12,4 +12,4 @@ joblib>=0.9.4
 keyring
 keyrings.alt    # for alternative keyring implementations
 dill
-setuptools>=11.3
+setuptools>=36.3