Merge pull request #997 from ethereum-optimism/nav-airdrop-4

Update config.js with airdrop 4

src/.vuepress/config.js

@@ -179,6 +179,7 @@ module.exports = {
             '/docs/governance/howto-delegate.md',
             '/docs/governance/economics.md',
             '/docs/governance/allocations.md',
+            '/docs/governance/airdrop-4.md',
             '/docs/governance/airdrop-3.md',
             '/docs/governance/airdrop-2.md',
             '/docs/governance/airdrop-1.md'