fix ftplib resource warnings
diff --git a/Lib/ftplib.py b/Lib/ftplib.py
index 50dbacc..22b5fd2 100644
--- a/Lib/ftplib.py
+++ b/Lib/ftplib.py
@@ -361,6 +361,7 @@
             conn, sockaddr = sock.accept()
             if self.timeout is not _GLOBAL_DEFAULT_TIMEOUT:
                 conn.settimeout(self.timeout)
+            sock.close()
         if resp[:3] == '150':
             # this is conditional in case we received a 125
             size = parse150(resp)