build(yarn): Upgrade to 1.13.0 and enforce version

[billyvg]

We can enforce consistent yarn version by checking in a yarn release into the repo and defining the yarn release to use in .yarnrc.

See https://yarnpkg.com/en/docs/cli/policies for more information

[billyvg]

@mattrobenolt thoughts on checking in yarn into the repo? It'll guarantee that the yarn version used across developers and build tools will be in sync.

[mattrobenolt]

You don't want my opinions.

[billyvg]

Closing this as it seems clunky having to vendor yarn - there's not been any significant features that we use where we would need to enforce a specific yarn version.