fix linter warnings

5 jobs for master in 2 minutes and 31 seconds (queued for 1 second)
Status Name Job ID Coverage
  Lint
passed black #613118

00:00:25

passed cpplint #613119

00:00:20

passed flake8 #613117

00:00:28

 
  Deploy
passed pages #613120

00:01:45

passed pages:deploy

00:00:01