Use npm v6.1.0

[netweb]

We should use the latest stable release of npm, this is the v6 branch, the current version is 6.1.0

Using a standardised version of npm allows developers contributing to core to have a common local configuration eliminating potential lock file compatibilities that can occur when using npm v5 vs v6

This will also require a systems request for the build server to be updated to npm 6.1.0, currently, the build server is using npm 5.5.1, see ​https://make.wordpress.org/systems/2017/12/11/node-js-8-x-on-build-server/

Related: #35105 / [42461]

[netweb]

Example Systems Request: ​https://make.wordpress.org/systems/

Use npm 6.1.0 on build server

Hi, as per #44245-core could we please have the npm version 6.1.0 release installed on WordPress.org?

This will be needed for WordPress 5.0 & Gutenberg (once merged) for build scripts to operate.

Currently we have npm 5.5.1

#prio2

[azaozz]

In 43320:

Build tools: Use npm v6.1.0.

Props netweb.
Fixes #44245.

[pento]

Posted to make/systems: ​https://make.wordpress.org/systems/2018/05/28/upgrade-node-npm-on-build-server/

[jorbin]

committed to 5.0 in [43684]