错误信息： The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99.
解决方案：进入target的build setting 栏，修改iOS Deployment Target为8.0以上
还有种做法，是在Podfile文件最底部添加，后边的版本号就跟错误提示中说明的版本号
post_installdo|installer|
installer.pods_project.targets.eachdo|target|
target.build_configurations.eachdo|config|
ifconfig.build_settings['IPHONEOS_DEPLOYMENT_TARGET'].to_f <9.0
config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] ='9.0'
end
end
end
end
