updated travis

.travis.yml

@@ -2,10 +2,10 @@ language: python
 sudo: false
 python:
 - '3.6'
+services:
+  - xvfb # https://benlimmer.com/2019/01/14/travis-ci-xvfb/
 before_script:
-- if [ ${TRAVIS_PYTHON_VERSION} == '3.6' ]; then pip install flake8; flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics; fi
 - "export DISPLAY=:99.0"  # https://docs.travis-ci.com/user/gui-and-headless-browsers
-- sh -e /etc/init.d/xvfb start
 - sleep 3
 install:
 - wget http://repo.continuum.io/miniconda/Miniconda-latest-Linux-x86_64.sh -O miniconda.sh