Clean-up gulp

This gulp task was not very friendly with a non orphan branch.

Look at what I did for ``gh-pages`` in the source tree. That's why I do for many repos, and it works well.

Releasing consists in:

```
$ git checkout gh-pages
$ git merge vX.Y.Z
$ make dist
$ git commit --amend build/daybed.js
$ git push origin gh-pages
```