升级私有库时，MBProgressHUD中的build setting中的iOS deployment target会变成4.3

原因:pod update is setting the deployment target of the pod to iOS 4.3 because that is the default deployment target if the podspec doesn't specify one. This was an intentional decision by the CocoaPods team, even though it breaks some older pods that basically have an incomplete podspec. If you are maintaining the pod, you should specify an appropriate target, e.g. platform :ios, '8.0' to fix it. If you are just trying to use a pod that is broken in this way, please try my suggestion below

大致意思是MBProgressHUD中没有在podspec中设置默认的default deployment target

解决方案有两种：

       第一种：

升级MBProgressHUD

        第二种：

       在podfile后面添加如下暴力代码：

post_install do |installer|

  installer.pods_project.targets.each do |target|

    target.build_configurations.each do |config|

      config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '9.2'

    end

  end

end