Update yaml dependency to version 2

[QuintinWillison]

I just had a quick run at this at 0bafbc3 but got the following failure on npm run build:

/Users/quintinwillison/code/ably/features/build.js:313
      throw new Error(`Unhandled YAML AST node type "${nodeType}".`);
      ^

Error: Unhandled YAML AST node type "undefined".
    at validateStructure (/Users/quintinwillison/code/ably/features/build.js:313:13)
    at Object.<anonymous> (/Users/quintinwillison/code/ably/features/build.js:37:1)
    at Module._compile (node:internal/modules/cjs/loader:1103:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1157:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
    at node:internal/main/run_main_module:17:47Possibly as a result of https://github.com/eemeli/yaml/issues/173 from a quick scan of the [version 2.0.0 release notes for `yaml`](https://github.com/eemeli/yaml/releases/tag/v2.0.0).

We don't have the time to tackle this right now, so am deferring to backlog by creating this issue.

┆Issue is synchronized with this Jira Uncategorised by Unito