Make test_getoutput work on Windows.

Author: benjaminp

test_six.py

@@ -233,8 +233,8 @@ def test_map():
 
 def test_getoutput():
     from six.moves import getoutput
-    output = getoutput('echo "foo"')
-    assert output == 'foo'
+    output = getoutput('dir' if sys.platform.startswith('win') else 'echo foo')
+    assert output != ''
 
 
 def test_zip():