See #2251 (review): BIP3 changed the criteria for BIP types; under new criteria, the descriptor BIPs belong to the "Specification" type. This PR updates all the BIPs from bip379 to bip390, excluding bip388, since it already has the right type.
Note that bip380 to bip387 are already in the "Deployed" status, and BIP3 specifies that modifications beyond minor amendments should be avoided. I think it's still okay to change the type of these, but wanted to flag in case people think it's not minor, and should be avoided.
