sshfs: make _finalize method static to allow garbage collection (#62)

Author: skshetry

sshfs/spec.py

@@ -100,7 +100,8 @@ async def _connect(
 
     connect = sync_wrapper(_connect)
 
-    async def _finalize(self, pool, stack):
+    @staticmethod
+    async def _finalize(pool, stack):
         await pool.close()
 
         # If an error occurs while the SSHFile is trying to