Really fix bug

Lib/test/test_urllib.py

@@ -118,8 +118,8 @@ class ProxyTests(unittest.TestCase):
         # Records changes to env vars
         self.env = support.EnvironmentVarGuard()
         # Delete all proxy related env vars
-        for k in os.environ.keys():
-            if k == 'NO_PROXY':
+        for k in list(os.environ):
+            if 'proxy' not in k.lower():
                 self.env.unset(k)
 
     def tearDown(self):