[docs] update wrangler.toml example to wrangler@2

[EstebanBorai]

Updates the example provided for wrangler.toml file for
the adapter-cloudflare-workers documentation, to follow
the specs on wrangler@2.

Changes from Cloudflare include:

• The type key is no longer needed.
• The zone_id is unnecessary since they can deduce this from routes directly.
• The compatibility_date is required when publishing.
• The main key belongs to the global scope, instead of the build.upload section
• The format key is inferred automatically from the code.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 3d8ef40

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/adapter-cloudflare-workers	Patch

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[benmccann]

@EstebanBorai are there also changes needed to the adapter-cloudflare readme in addition to adapter-cloudflare-workers?

[EstebanBorai]

Hi @benmccann! As far as I have been able to test no.

Given that the adapter-cloudflare is intended for Cloudflare Pages, theres no need to provide a wrangler.toml yourself.

[Rich-Harris]

Thanks! I made some further changes — the README was quite out of date, and it turns out we can simplify it quite a bit