warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 6.0, but the range of supported deployment target versions is 8.0 to 13.2.99.

 warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 6.0, but the range of supported deployment target versions is 8.0 to 13.2.99. (in target 'Reachability' from project 'Pods')
    warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 4.3, but the range of supported deployment target versions is 8.0 to 13.2.99. (in target 'FMDB' from project 'Pods')
    warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 4.3, but the range of supported deployment target versions is 8.0 to 13.2.99. (in target 'Toast' from project 'Pods')
    warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 7.0, but the range of supported deployment target versions is 8.0 to 13.2.99. (in target 'AFNetworking' from project 'Pods')
    warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 6.0, but the range of supported deployment target versions is 8.0 to 13.2.99. (in target 'libwebp' from project 'Pods')

解决方法：在ios下的Podfile 文件的 post_install do |installer|部分进行以下的替换就会消失

post_install do |installer|
  installer.pods_project.targets.each do |target|
 target.build_configurations.each do |config|
  if config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'].to_f < 8.0
    config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '8.0'
     end
   end
  end
end

　　参考：https://www.jianshu.com/p/226832903157