Cannot build for macOS using CocoaPods

[edwinveger]

When installing SwiftOCR through CocoaPods, it depends on the CocoaPods version of GPUImage (instead of the repository version). For macOS, this does not compile since there are several files missing in GPUImage that SwiftOCR relies upon. These files are explicitly excluded from the OSX pod.

Step to reproduce:

1. create a new Xcode project with macOS CLI target.
2. Install `pod 'SwiftOCR'.
3. Try to build.

I have tried to work around this by manually building the frameworks directly from the repository (not through), but got some obscure errors at runtime when importing them 😕 so I had to resort to posting an issue here. I suspect this might be fixed by pinning to a specific revision of the GPUImage pod dependency, but I haven't figured out which exactly.