Change Couchbase repo to main repo

[benofben]

Currently the link is pointing to Couchbase Lite. I've changed it to point to our main repo for the core database. Alternative, we could have this link point to https://github.com/couchbase, though I'm not sure if you need specific repos rather than orgs here.

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[dankohn]

Thanks for the fix.

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[benofben]

LGTM