[fix] flake8 verison
diff --git a/.travis.yml b/.travis.yml
index 0b3b49f..beab4e1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,6 +15,8 @@
   - mysql
 
 install:
+  - pip install flake8==3.3.0
+  - flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics
   - sudo rm /etc/apt/sources.list.d/docker.list
   - sudo apt-get purge -y mysql-common mysql-server mysql-client
   - nvm install v7.10.0