[#440] Update travis config (#441)
[#440] Update travis config (#441)

Changed `npm install` to `npm ci` to install dependencies based on lock
file versions.

Changed `npm run eslint` to `npm run prettier` since `npm run eslint`
was removed from package.json and was calling prettier to begin with.
jenkoian/hacktoberfest-checker,jenkoian/hacktoberfest-checker,jenkoian/hacktoberfest-checker,jenkoian/hacktoberfest-checker