Specs satisfying the `Alamofire (~> 5.0.0-beta.3)` dependency were found, but they required a hig...

用 pod install 时 报错

[!] CocoaPods could not find compatible versions for pod "Alamofire":
    In Podfile:
   Alamofire (~> 5.0.0.beta.1)

Specs satisfying the `Alamofire (~> 5.0.0.beta.1)` dependency were 
found, but they required a higher minimum deployment target.

原因是Alamofire5.0.0.beta.1最低支持10.0 ，把 platform :ios, ‘8.0’改成platform :ios, ‘10.0’，就万事大吉了！！！

platform :ios,'10.0'
use_frameworks!
target 'Test' do
pod 'Alamofire', '~> 5.0.0-beta.3'
end

alamofire5.0.0.beta.1为什么不支持 ios7 | ios8 | ios9?

大神说：他们讨论过，他们用了iOS10的一些API，更安全。然后权衡后就放弃了iOS8了。重点是： 他们不会再去支持iOS8了！