目前安装的版本是Cocoapods的0.37.2，xcode6.3.
尝试了各种 卸载重装还是没解决问题，降pod版本后也报错又重新装回0.37

pod install 之后

Analyzing dependencies

CocoaPods 0.38.0.beta.2 is available.
To update use: gem install cocoapods --pre
[!] This is a test version we'd love you to try.

For more information see http://blog.cocoapods.org
and the CHANGELOG for this version http://git.io/BaH8pQ.

Downloading dependencies
Installing HexColors (2.2.1)
Installing LBBlurredImage (0.2.2)
Installing LlamaKit (0.1.1)
Installing Mantle (2.0.2)
Installing ReactiveCocoa (3.0.0-alpha.1)
Installing TSMessages (0.9.12)
[!] Pods written in Swift can only be integrated as frameworks; this feature is still in beta. Add use_frameworks! to your Podfile or target to opt into using it.

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任务完成之后文件夹内也没有生成xcworkspace。
下面是Podfile：
source 'https://github.com/CocoaPods/Specs.git'

platform :ios, ‘8.0’

xcodeproj 'SimpleWeather'
target "SimpleWeather" do
pod 'Mantle', '~> 2.0.2'
pod 'LBBlurredImage', '~> 0.2.2'
pod 'TSMessages', '~> 0.9.12'
pod 'ReactiveCocoa', '~> 3.0.0-alpha.1'
end

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你需要在 Podfile 最开始加上 use_frameworks!。现在的状况是 pod install 报错了，没有走完所有的流程，所以没有生成 workspace 文件。