You could just install,

$ npm install -g vue-cli-ghpages
$ npm run build
$ sudo vue-cli-ghpages

the shorthand for this is,

$ sudo vcg

This way you will not need to create a gh-pages branch

But remember to on the master branch, in config/index.js change the build object (NOT to ‘dev’ object) property assetsPublicPath to,

assetsPublicPath: './',

or you can change it to,

assetsPublicPath: '/repo-name/dist/',

or to,

assetsPublicPath: 'https://user-name.github.io/repo-name',

Navigate to the repo’s gh-pages with,

https://user-name.github.io/repo-name/

Don’t forget the trailing forward slash at the end of this url.

To update the project,

$ git add .
$ git commit -m "updated commit"
$ git push origin master
$ npm run build
$ sudo vcg

Again navigate to,

https://user-name.github.io/repo-name

and a few hard refreshes may be necessary.

Also it may take a few moments for gh-pages to update.