proxyconfig_stem pylint fixes

src/plugins/proxyconfig_stem.py

@@ -1,5 +1,8 @@
 # -*- coding: utf-8 -*-
-
+"""
+src/plugins/proxyconfig_stem.py
+===================================
+"""
 import os
 import logging
 import random  # noseq
@@ -29,7 +32,7 @@ class DebugLogger(object):
             # Plugin's debug or unexpected log line from tor
             self._logger.debug(line)
         else:
-            self._logger.log(self._levels.get(level, 10), '(tor)' + line)
+            self._logger.log(self._levels.get(level, 10), '(tor) %s', line)
 
 
 def connect_plugin(config):  # pylint: disable=too-many-branches