fix: update Node.js requirement to >=20.18.1

undici@7.x requires Node 20.18.1+ due to global File class dependency.

Fixes #109

Author: andris9

README.md

@@ -15,7 +15,7 @@
 - **BIMI** resolving and **VMC** validation
 - **MTA-STS** helper functions
 
-mailauth is a pure JavaScript implementation, requiring no external applications or compilation. It runs on any server or device with Node.js version 18 or later.
+mailauth is a pure JavaScript implementation, requiring no external applications or compilation. It runs on any server or device with Node.js version 20.18.1 or later.
 
 > [!NOTE]
 > mailauth is used by [EmailEngine](https://emailengine.app/) for validating email authentication settings. See the [Email Authentication Testing documentation](https://learn.emailengine.app/docs/advanced/email-authentication-testing) for details.

package.json

@@ -58,7 +58,7 @@
         "yargs": "17.7.2"
     },
     "engines": {
-        "node": ">=18.0.0"
+        "node": ">=20.18.1"
     },
     "bin": {
         "mailauth": "bin/mailauth.js"