ci: test Node.js 6, 8, 10 and 11 (#384)
ci: test Node.js 6, 8, 10 and 11 (#384)

* ci: test Node.js 6, 8, 10 and 11

* ci: remove allowed_failures as all tests are green

kvz/phpjs,kvz/phpjs,kvz/phpjs,kvz/phpjs