Update dependency gulp to v4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change	References
gulp	devDependencies	major	3.9.1 -> 4.0.0	homepage, source

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Release Notes

gulpjs/gulp

v4.0.0

Compare Source

Task system changes

• replaced 3.x task system (orchestrator) with new task system (bach)
  • removed gulp.reset
  • removed 3 argument syntax for gulp.task
  • gulp.task should only be used when you will call the task with the CLI
  • added gulp.series and gulp.parallel methods for composing tasks. Everything must use these now.
  • added single argument syntax for gulp.task which allows a named function to be used as the name of the task and task function.
  • added gulp.tree method for retrieving the task tree. Pass { deep: true } for an archy compatible node list.
  • added gulp.registry for setting custom registries.

CLI changes

• split CLI out into a module if you want to save bandwidth/disk space. you can install the gulp CLI using either npm install gulp -g or npm install gulp-cli -g, where gulp-cli is the smaller one (no module code included)
• add --tasks-json flag to CLI to dump the whole tree out for other tools to consume
• added --verify flag to check the dependencies in package.json against the plugin blacklist.

vinyl/vinyl-fs changes

• added gulp.symlink which functions exactly like gulp.dest, but symlinks instead.
• added dirMode param to gulp.dest and gulp.symlink which allows better control over the mode of the destination folder that is created.
• globs passed to gulp.src will be evaluated in order, which means this is possible gulp.src(['*.js', '!b*.js', 'bad.js']) (exclude every JS file that starts with a b except bad.js)
• performance for gulp.src has improved massively
  • gulp.src(['**/*', '!b.js']) will no longer eat CPU since negations happen during walking now
• added since option to gulp.src which lets you only match files that have been modified since a certain date (for incremental builds)
• fixed gulp.src not following symlinks
• added overwrite option to gulp.dest which allows you to enable or disable overwriting of existing files

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[coveralls]

Coverage remained the same at 81.25% when pulling 7cd6c99 on renovate/gulp-4.x into 4284b0a on master.