fix(create-instantsearch-app): fix corejs version in vue-is template

[shaejaz]

Summary
Using the vue instantsearch template with the create-instantsearch-app results in a dependency error when running yarn start. This fixes the core-js version to prevent that.

TODO:

• Check if other templates have the same error

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Latest deployment of this branch, based on commit 4b42421:

Sandbox	Source
example-instantsearch-getting-started	Configuration
example-react-instantsearch-getting-started	Configuration
example-react-instantsearch-next-app-dir-example	Configuration
example-react-instantsearch-next-routing-example	Configuration
example-vue-instantsearch-getting-started	Configuration