Update GPUImage.podspec
Enable `pod lib lint` in Travis configuration
Silence `pod setup`
leak fixed with GCG under iOS 6.0.

https://github.com/CocoaPods/Specs/issues/1730
https://github.com/BradLarson/GPUImage/issues/1748
It's not working like what I thought.
Leak fixed if worked with cocoapods.

https://github.com/BradLarson/GPUImage/issues/1748
https://github.com/CocoaPods/CocoaPods/issues/1001
#1754 fixed problem form this issue. Changed runLoopMode.
fix use GPUImageFilterPipeline chain filters will cause GPUImageLowPassFilter not work
Merge pull request #1760 from aidenluo177/master

fix use GPUImageFilterPipeline chain filters will cause GPUImageLowPassF...
Merge pull request #1751 from demon1105/master

leak fixed when worked with cocoapods.
Merge pull request #1756 from chajcu/master

#1754 fixed problem form this issue. Changed runLoopMode.
Merge pull request #1702 from 52doho/patch-1

Update GPUImage.podspec
Merge pull request #1722 from rivera-ernesto/travis

Update Travis configuration