BIP 3 lists MIT-0 as an acceptable license, but scripts/buildtable.pl does not include it in %AcceptableLicenses. As a result, a BIP using License: MIT-0 would be rejected by the table validator even though the license is explicitly permitted by BIP 3.
Add MIT-0 to the validator's acceptable-license set so the script matches the current BIP process specification.
This is a one-line validator-only change.
