src: use nullptr in node_buffer.cc

Signed-off-by: gengjiawen <technicalcute@gmail.com>

PR-URL: #25820
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

src/node_buffer.cc

@@ -99,7 +99,7 @@ class CallbackInfo {
                                   Local<ArrayBuffer> object,
                                   FreeCallback callback,
                                   char* data,
-                                  void* hint = 0);
+                                  void* hint = nullptr);
  private:
   static void WeakCallback(const WeakCallbackInfo<CallbackInfo>&);
   inline void WeakCallback(Isolate* isolate);