Make gulp workable into Yarn's PnP mode

[bhanubais]

Now yarn reached at it's version 3.0.0 and gulp reached at 4.0.2
But gulp is still not working in yarn's default PnP (plug and play) mode.

To run gulp in yarn we have to change yarn's mode from pnp to node-modules as follow.

1. insert nodeLinker: node-modules into .yarnrc.yml file.
2. run yarn install
3. now you can run gulp.

But we lost plug and play feature of yarn and almost every package placed in two places one copy into .yarn folder and another one into node_modules folder.

There is no doubt that yarn did a great job to make dependencies neat and clean. It's also very fast compare to npm.
But an excited user can't just install latest NodeJs, Yarn, Gulp and hope gulp will run. Because by default Yarn run on PnP mode.

In the current scenario, we have to install package into .yarn as well as into node_modules to run gulp command. If gulp will agree upon to run on PnP mode we don't need to waste double storage.

[phated]

In yarnpkg/berry#3318 - yarn seems to claim that pnp support exists for gulp 4, so I'm going to close this.