NextApiResponse: setHeader() and writeHead() should return this (#144)

* setHeader() and writeHead() should return `this`

* Sync

---------

Co-authored-by: Frank <wangfanjie@gmail.com>

Author: Tietew

.changeset/twenty-hounds-refuse.md

@@ -0,0 +1,5 @@
+---
+"open-next": patch
+---
+
+Response: setHeader() and writeHead() return "this"

packages/open-next/src/adapters/response.ts

@@ -70,6 +70,7 @@ export class ServerResponse extends http.ServerResponse {
     } else {
       super.setHeader(key, value);
     }
+    return this;
   }
 
   writeHead(statusCode, reason, obj) {
@@ -85,7 +86,7 @@ export class ServerResponse extends http.ServerResponse {
       }
     }
 
-    super.writeHead(statusCode, reason, obj);
+    return super.writeHead(statusCode, reason, obj);
   }
 
   constructor({ method }) {