update kit peerDependency on svelte to ^3.39.0

[dominikg]

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svelte 3.39.0 introduced a new export svelte/ssr with a noop for onMount
sveltejs/svelte#6372
which is supported by vite-plugin-svelte sveltejs/vite-plugin-svelte#74

To make sure users do profit from this improvement, raise the peer dependency version.
Example of a user with older svelte version: #2181

[changeset-bot]

🦋 Changeset detected

Latest commit: 2779a33

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[dominikg]

would this be a breaking change?

[benmccann]

I suppose it's breaking, but that doesn't mean a whole lot given our beta phase. We can just apply the label to help people find it more easily

Any reason this is marked as draft?

[dominikg]

the fact that it is breaking and i wanted to make sure it's seen/discussed before merge.