新增: pull_created_unix字段至新接口

app/views/api/v1/projects/pulls/_simple_detail.json.jbuilder

@@ -23,4 +23,5 @@ json.issue do
 end
 
 json.reviewers pull.reviewers.pluck(:login)
-json.journals_count pull.journals.count
+json.journals_count pull.journals.count
+json.pr_created_unix pull.created_at.to_i