Upgrade Matrix for 6.x incorrect states 3.x -> 5.x is supported

The matrix on https://docs.couchbase.com/server/6.0/install/upgrade.html#supported-upgrade-paths-2 is incorrect.

It says that you can go from 3.x -> 5.x -> 6.x.

However, 3.x -> 5.x is not a compatible upgrade and specifically is not listed under https://docs.couchbase.com/server/5.5/install/upgrade.html#supported-upgrade-paths.

The path should be 3.x -> 4.x -> 5.x -> 6.x.