Merge pull request readthedocs#2004 from rtfd/upgrade-setuptools

Bump setuptools to latest

Author: ericholscher

readthedocs/doc_builder/python_environments.py

@@ -99,7 +99,7 @@ def install_core_requirements(self):
         requirements = [
             'sphinx==1.3.5',
             'Pygments==2.0.2',
-            'setuptools==18.6.1',
+            'setuptools==20.1.1',
             'docutils==0.12',
             'mkdocs==0.15.0',
             'mock==1.0.1',