re-add cocoapod build result to linked libraries (fixes link error)

Without this change I am not able to build Hammerspoon using Xcode 6.1.1.
The cocoapod library is not found because the dependency to the build result is somehow broken.
To fix this I re-added the static lib to the linked libraries.

I am not sure if this issue is related to Xcode 6.1.1 because the Travis CI seems to be able to build Hammerspoon without a problem...

@cmsj does the error also occur in your builds?