Travis: Don't use `npm ci` as it doesn't exist in the npm included in Node 10
Travis: Don't use `npm ci` as it doesn't exist in the npm included in Node 10

It will be included in Node 10.1 or later but npm already plans to alias
`npm install` to `npm ci` internally when possible[1] so that should no longer
be an issue.

[1]: https://blog.npmjs.org/post/173239798780/beyond-npm6-the-future-of-the-npm-cli

mgol/eslint-config-mgol,mzgol/eslint-config-mzgol