Deploy to GitHub Pages using Travis CI and deploy keys – https://medium.com/@simon.legner/deploy-to-github-pages-using-travis-ci-and-deploy-keys-db84fed7a929

.travis-deploy.sh

#!/bin/sh
set -e

# setup ssh-agent and provide the GitHub deploy key
eval "$(ssh-agent -s)"
openssl aes-256-cbc -K $encrypted_dc4c0df7bb33_key -iv $encrypted_dc4c0df7bb33_iv -in id_ed25519.enc -out id_ed25519 -d
chmod 600 id_ed25519
ssh-add id_ed25519

# commit the assets in build/ to the gh-pages branch and push to GitHub using SSH
./node_modules/.bin/gh-pages -d build/ -b gh-pages -r git@github.com:${TRAVIS_REPO_SLUG}.git

.travis.yml

language: node_js

node_js:
  - node

script:
  # test/lint and build the project
  - npm run lint
  - npm run build

deploy:
  - provider: script
    skip_cleanup: true # do not delete the built assets
    script: ./.travis-deploy.sh
    on:
      branch: master