Use WindowsPlatformSettings for cywgin

BUG=https://github.com/catapult-project/catapult/issues/3558

Review-Url: https://codereview.chromium.org/2878053004 .
diff --git a/platformsettings.py b/platformsettings.py
index 81cb56c..9037ff8 100644
--- a/platformsettings.py
+++ b/platformsettings.py
@@ -767,7 +767,7 @@
     return _LinuxPlatformSettings()
   if system == 'Windows' and release == 'XP':
     return _WindowsXpPlatformSettings()
-  if system == 'Windows':
+  if system == 'Windows' or system.startswith('CYGWIN'):
     return _WindowsPlatformSettings()
   if system == 'FreeBSD':
     return _FreeBSDPlatformSettings()