Fix TS error.

src/lib/middleware.ts

@@ -21,7 +21,7 @@ const log = debug('umami:middleware');
 export const useCors = createMiddleware(
   cors({
     // Cache CORS preflight request 24 hours by default
-    maxAge: process.env.CORS_MAX_AGE || 86400,
+    maxAge: Number(process.env.CORS_MAX_AGE) || 86400,
   }),
 );