If you have a custom domain, you may have to copy the CNAME file after every Jekyll build.
You can use the
keep_files option in
_config.yml to prevent the CNAME file in the
_site directory from being deleted during the build process.
If you are using Travis CI, you can copy the CNAME file to the
_site directory after the build process. Here’s a sample
.travis.yml configuration that you can use: