fixed a bug in push back list; close #1298

src/parse.y

@@ -3293,7 +3293,7 @@ peek_n(parser_state *p, int c, int n)
     list = push(list, (node*)(intptr_t)c0);
   } while(n--);
   if (p->pb) {
-    p->pb = push(p->pb, (node*)list);
+    p->pb = append(p->pb, (node*)list);
   }
   else {
     p->pb = list;