Merge pull request #16235 from a-musing-moose/master

adding python version environmental markers in the new style
diff --git a/setup.py b/setup.py
index 388e629..b87843f 100644
--- a/setup.py
+++ b/setup.py
@@ -276,11 +276,11 @@
 }
 
 INSTALL_REQUIRES = (
-    'six>=1.5.2',
+    "six>=1.5.2",
+    "futures>=2.2.0 ; python_version<'3.2'",
+    "enum34>=1.0.4 ; python_version<'3.4'"
 )
 
-if not PY3:
-  INSTALL_REQUIRES += ('futures>=2.2.0', 'enum34>=1.0.4')
 
 SETUP_REQUIRES = INSTALL_REQUIRES + (
     'sphinx>=1.3',