add server.init() to adapter-vercel

Required since sveltejs/kit#6179, as hooks.js
are initialized in server.init()

Author: SG60

adapter-vercel/files/edge.js

@@ -6,7 +6,11 @@ const server = new Server(manifest);
 /**
  * @param {Request} request
  */
-export default (request) => {
+export default async (request) => {
+	await server.init({
+		env: process.env
+	});
+
 	return server.respond(request, {
 		getClientAddress() {
 			return request.headers.get('x-forwarded-for');