chore: Temporarily disable flake rule F821
diff --git a/.travis.yml b/.travis.yml
index 26a4caa..2e3a1e7 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,7 +16,7 @@
   # fix mongodb travis error
   - sudo rm /etc/apt/sources.list.d/mongodb*.list
   - pip install flake8==3.3.0
-  - flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics
+  - flake8 . --count --select=E901,E999,F822,F823 --show-source --statistics
   - sudo rm /etc/apt/sources.list.d/docker.list
   - sudo apt-get install hhvm && rm -rf /home/travis/.kiex/
   - sudo apt-get purge -y mysql-common mysql-server mysql-client