bisect-kit: fix lint warnings

BUG=None
TEST=pylint

Change-Id: I2add8a04b49d7cc432f138c6d0b76eb880485b98
diff --git a/bisect_kit/android_util.py b/bisect_kit/android_util.py
index f1ca031..3bf3ee0 100644
--- a/bisect_kit/android_util.py
+++ b/bisect_kit/android_util.py
@@ -59,7 +59,7 @@
   # Fetching android build data directly will fail without authentication.
   # Following code is just serving as demo purpose. You should modify or hook
   # it with your own implementation.
-  logger.warn('fetch_android_build_data need to be hooked')
+  logger.warning('fetch_android_build_data need to be hooked')
   from six.moves import urllib
   try:
     return urllib.request.urlopen(url).read().decode('utf8')