always install "distributed" on Windows

Author: basnijholt

setup.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 
+import os
 import sys
 
 from setuptools import find_packages, setup
@@ -30,6 +31,10 @@ def get_version_and_cmdclass(package_name):
     "atomicwrites",
 ]
 
+if os.name == 'nt':  # on Windows
+    # distributed provides the default executor on Windows
+    install_requires.append("distributed")
+
 extras_require = {
     "notebook": [
         "ipython",