Update documented Node.js support version to 20 (#1347)

Co-authored-by: Can Çitoğlu <cancit@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

packages/node/README.md

@@ -10,7 +10,7 @@ https://www.npmjs.com/package/@segment/analytics-node
 
 
 ## Runtime Support
-- Node.js >= 18
+- Node.js >= 20
 - AWS Lambda
 - Cloudflare Workers
 - Vercel Edge Functions