Could not find JSON in http://updates.jenkins-ci.org/update-center.json?id=default&version=2.7.4

14-Sep-2016 21:43:58.241 INFO [Download metadata thread] hudson.model.AsyncPeriodicWork$1.run Finished Download metadata. 2,388 ms
14-Sep-2016 21:43:59.070 WARNING [Jenkins initialization thread] hudson.model.UpdateCenter.updateDefaultSite Upgrading Jenkins. Failed to update the default Update Site 'default'. Plugin upgrades may fail.
 java.io.IOException: Could not find JSON in http://updates.jenkins-ci.org/update-center.json?id=default&version=2.7.4
        at hudson.model.DownloadService.loadJSON(DownloadService.java:174)
        at hudson.model.UpdateSite.updateDirectlyNow(UpdateSite.java:176)
        at hudson.model.UpdateCenter.updateDefaultSite(UpdateCenter.java:2181)
        at jenkins.install.SetupWizard.init(SetupWizard.java:170)
        at jenkins.install.InstallState$3.initializeState(InstallState.java:105)
        at jenkins.model.Jenkins.setInstallState(Jenkins.java:970)
        at jenkins.install.InstallUtil.proceedToNextStateFrom(InstallUtil.java:94)
        at jenkins.model.Jenkins.<init>(Jenkins.java:887)
        at hudson.model.Hudson.<init>(Hudson.java:85)
        at hudson.model.Hudson.<init>(Hudson.java:81)
        at hudson.WebAppMain$3.run(WebAppMain.java:227)

14-Sep-2016 21:43:59.097 INFO [Jenkins initialization thread] hudson.WebAppMain$3.run Jenkins is fully up and running

　　瀏覽器輸http://updates.jenkins-ci.org/update-center.json?id=default&version=2.7.4發現跳轉到清華大學的一個代理服務器上了https://mirrors.tuna.tsinghua.edu.cn/jenkins/updates/current/update-center.json

而這個代理好像抽風了，不知道是不是鏈接取消了，打不開