CNAME file not copied in gh-pages branch after npm run deploy

Question

I have a react app deployed with git hub pages, using gh-pages plugin. My package.json entry look like this.

"scripts": {
    "predeploy": "npm run build",
    "deploy": "gh-pages -d build”,
     .....
   }

Eveything worked fine until I tried to use a custom domain.

1. I configured the required A and CNAME entry in my domain provider DNS settings.

2. I created the CNAME file in the develop branch. That is the branch that I have checked out on my local machine.

3. I run npm run deploy on develop branch on local machine.

4. plugin pushed the build code to gh-pages branch on remote.

5. the gh-pages branch on remote does not contain the CNAME file.

6. after every deploy I have to manually add the custom-domain from github settings pages section, which eventually create a CNAME file. And then every works.

Is there a configuration requied in package.json to force gh-pages plugin to copy the CNAME file ?