[ci] Run the lint script only once

Author: lpinca

.travis.yml

@@ -9,5 +9,8 @@ os:
   - linux
   - osx
   - windows
+script:
+  - if [ "${TRAVIS_NODE_VERSION}" == "14" ] && [ "${TRAVIS_OS_NAME}" == linux ]; then npm run lint; fi
+  - npm test
 after_success:
   - nyc report --reporter=text-lcov | coveralls