Observed new error:
Observed new error:

> sh: 0: Can't open /etc/init.d/xvfb
> The command "if [ "$TRAVIS_OS_NAME" == "linux"  ]; then export DISPLAY=:99.0; sh -e /etc/init.d/xvfb start; fi" failed and exited with 127 during .

REF: https://travis-ci.org/github/naokazuterada/MarkdownTOC/jobs/690562765

Added sleep as suggested in the official documentation:

REF: https://docs.travis-ci.com/user/gui-and-headless-browsers/#using-xvfb-to-run-tests-that-require-a-gui

naokazuterada/MarkdownTOC