NPM package config: set Node version constraint

[chalin]

This formally encode the Docsy project constraint that we officially support only the active LTS version of Node:

docsy/.nvmrc

Line 1 in 6f796f9

lts/*

[deining]

LGTM.

In this context, I would propose to also add (and pin) the node version in netlify.toml, thus getting more reproducible builds:

[build.environment]
NODE_VERSION = "18.14.2"
GO_VERSION = "1.19.5"
HUGO_THEME = "repo"

[chalin]

It is already constrained via https://github.com/google/docsy/blob/main/.nvmrc, which is better than adding a constraint in the Netlify config, as pointed out in https://docs.netlify.com/configure-builds/manage-dependencies/#node-js-and-javascript:

At this point I'm not looking to pin Node to a specific version. Any version of the Active LTS is what we're meant to support.

Let's keep things as dry as we can. The engines.node constraint is a lower bound -- if I could, I'd put the equivalent of lts/* but that doesn't seem possible. As you know we've had problems in the past with folks reporting issues that arose because they were using a version of Node that was far too old. This will help improve on that scenario.

[chalin]

Thanks for the feedback @deining. I'll merge this as is for now.