fix: LanguageMessages type now supports languages in TypeScript

Author: jacobkapitein

lib/index.d.ts

@@ -26,7 +26,7 @@ declare namespace Joi {
 
     type BasicType = boolean | number | string | any[] | object | null;
 
-    type LanguageMessages = Record<string, string>;
+    type LanguageMessages = Record<string, string | Record<string, string>>;
 
     type PresenceMode = 'optional' | 'required' | 'forbidden';