mypy_extensions are universal (#3764)

setup.cfg

diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..3c6e79c
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,2 @@
+[bdist_wheel]
+universal=1

setup.py

diff --git a/setup.py b/setup.py
index b0ffbc5..0ec4ba1 100644
--- a/setup.py
+++ b/setup.py
@@ -1,8 +1,6 @@
-#!/usr/bin/env python
-
 # NOTE: This package must support Python 2.7 in addition to Python 3.x
 
-from distutils.core import setup
+from setuptools import setup
 
 version = '0.3.0'
 description = 'Experimental type system extensions for programs checked with the mypy typechecker.'