到底怎么用 Pod 获取 Gmai 的 SDK

$ pod init

$pod 'Google-API-Client/Gmail', '~> 1.0'

$ pod install

Google的文档是这么说的，但是每次第二步就会有问题，更别说Install了，

ghost$ pod 'Google-API-Client/Gmail', '~> 1.0'
[!] Unknown command: Google-API-Client/Gmail,
Did you mean: plugins

Usage:

$ pod COMMAND

  CocoaPods, the Cocoa library package manager.

Commands:

+ init       Generate a Podfile for the current directory.
+ install    Install project dependencies to Podfile.lock versions
+ ipc        Inter-process communication
+ lib        Develop pods
+ list       List pods
+ outdated   Show outdated project dependencies
+ plugins    Show available CocoaPods plugins
+ repo       Manage spec-repositories
+ search     Searches for pods
+ setup      Setup the CocoaPods environment
+ spec       Manage pod specs
+ trunk      Interact with the CocoaPods API (e.g. publishing new specs)
+ try        Try a Pod!
+ update     Update outdated project dependencies and create new
             Podfile.lock

Options:

--silent     Show nothing
--version    Show the version of the tool
--verbose    Show more debugging information
--no-ansi    Show output without ANSI codes
--help       Show help banner of specified command

bogon:PortalWaitList ghost$ pod install
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
Generating Pods project
Integrating client project

[!] [!] The Podfile does not contain any dependencies.

具体应该怎么搞？
这是Gmail的文档网址
https://developers.google.com/gmail/api/quickstart/ios