Generate requirements list dynamically instead of using environment markers.
This allows using versions of setuptools older than 20.6.8.

diff -Nurp pdir2-0.2.2.orig/setup.py pdir2-0.2.2/setup.py
--- pdir2-0.2.2.orig/setup.py	2017-10-14 13:11:46.000000000 -0500
+++ pdir2-0.2.2/setup.py	2017-10-20 20:55:07.353242820 -0500
@@ -1,9 +1,17 @@
 import codecs
+import sys
+import platform
 from setuptools import setup
 
 readme = codecs.open('docs/README.rst', encoding='utf-8').read()
 history = codecs.open('docs/HISTORY.rst', encoding='utf-8').read()
 
+requirements = []
+if platform.system == 'Windows':
+    requirements.append('colorama')
+if sys.version_info[:2] < (3, 4):
+    requirements.append('enum34')
+
 setup(
     name='pdir2',
     version='0.2.2',
@@ -16,13 +24,9 @@ setup(
         'pdir',
     ],
     setup_requires=[
-        # minimum version to use environment markers
-        'setuptools>=20.6.8',
-    ],
-    install_requires=[
-        'colorama;platform_system=="Windows"',
-        'enum34;python_version<"3.4"',
+        'setuptools',
     ],
+    install_requires=requirements,
     include_package_data=True,
     license='MIT License',
     classifiers=[