Remove the need to install `gulp` globally
Update `dependencies`
Mark package as private

Ref: https://www.npmjs.org/doc/json.html#private
Clean up project

* Simplify build process and remove unneeded files.
* Move all files required to build the site into `src/`.
Update the browser logos

Ref: https://github.com/alrra/browser-logos
Make Travis automatically update `gh-pages` branch

Configure Travis to automatically update the content from the
`gh-pages` branch whenever something is pushed to the `master`
branch and the tests pass.