Update gulp to the latest version 🚀

The devDependency gulp was updated from `3.9.1` to `4.0.0`.

This version is not covered by your current version range.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

Release Notes for v4.0.0

Update

Remove graceful-fs from test suite (f27be05)

Docs

Remove references to gulp-util (fbc162f)
Fix the installation instructions (173a532)
Improve note about out-of-date docs (ec54d09)
Update recipes to install gulp@next (03b7c98)
Remove run-sequence from recipes (2eba29e)
Add installation instructions & update badges (76eb4d6)

Upgrade

Update glob-watcher (361ab63)

Build

Avoid broken node 9 (064d100)

Scaffold

Normalize repository (3011cf9)

Commits

The new version differs by 134 commits.

55eb23a Release: 4.0.0
173a532 Docs: Fix the installation instructions
ec54d09 Docs: Improve note about out-of-date docs
03b7c98 Docs: Update recipes to install gulp@next
2eba29e Docs: Remove run-sequence from recipes
76eb4d6 Docs: Add installation instructions & update badges
fbc162f Docs: Remove references to gulp-util
3011cf9 Scaffold: Normalize repository
f27be05 Update: Remove graceful-fs from test suite
361ab63 Upgrade: Update glob-watcher
064d100 Build: Avoid broken node 9
057df59 Release: 4.0.0-alpha.3
c1ba80c Breaking: Upgrade major versions of glob-watcher, gulp-cli & vinyl-fs
89acc5c Docs: Improve ES2015 task exporting examples (#1999)
0ac9e04 Docs: Add "Project structure" section to CONTRIBUTING.md (#1859)

There are 134 commits in total.

See the full diff

FAQ and help

There is a collection of [frequently asked questions](https://greenkeeper.io/faq.html). If those don’t help, you can always [ask the humans behind Greenkeeper](https://github.com/greenkeeperio/greenkeeper/issues/new).

Your Greenkeeper bot :palm_tree:

This change is

cinecove / defunctr