message: lint: Bump flake8 to 3.7.8
diff: export LC_ALL=C
  travis_retry pip3 install codespell==1.15.0
  -travis_retry pip3 install flake8==3.5.0
  +travis_retry pip3 install flake8==3.7.8
  travis_retry pip3 install vulture==0.29
  SHELLCHECK_VERSION=v0.6.0
  