Use latest LTS release for development (#222)

We now use the LTS release for development rather than a fixed version.
This makes it clear that we expect libraries to be updated to be
compatible with the latest LTS release, and reduces the frequency of
README/nvmrc updates needed.

.nvmrc

@@ -1 +1 @@
-v16
+lts/*

README.md

@@ -47,7 +47,7 @@ See our documentation:
 
 ### Setup
 
-- Install [Node.js](https://nodejs.org) version 16
+- Install the current LTS version of [Node.js](https://nodejs.org)
   - If you are using [nvm](https://github.com/creationix/nvm#installation) (recommended) running `nvm use` will automatically choose the right node version for you.
 - Install [Yarn v3](https://yarnpkg.com/getting-started/install)
 - Run `yarn install` to install dependencies and run any required post-install scripts