Add missing newline on dbt Cloud conn string example

[joellabes]

The Connecting to dbt Cloud page has a code block which is not rendering correctly:

This PR adds the missing newline so that it will be properly treated as a code block.

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^ Add meaningful description above
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[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.