Cocoapods error resolution.

This fixes an error for a deprecated command in the podspec file.
-mevdev

p.s. My current podFile has:   pod 'Playhaven-SDK', :git => 'https://github.com/mevdev/sdk-ios'
p.p.s. Error it fixes:

$ pod install
Analyzing dependencies

CocoaPods 0.34.1 is available.
To update use: gem install cocoapods\n
Pre-downloading: `PlayHaven-SDK` from `https://github.com/playhaven/sdk-ios/`

[!] Invalid `PlayHaven-SDK.podspec` file: [!] [Playhaven-SDK (1.13.0)] Clean paths are deprecated. CocoaPods now cleans unused files by default. Use the `preserve_paths` attribute if needed.. Updating CocoaPods might fix the issue.