Move generated OSX library naming to use dylib extension

[tfcollins]

This was a requested change we added to libiio starting here: https://github.com/analogdevicesinc/libiio/blob/f79c01beb276a67c8527a05baa09f00680bea37f/CI/travis/before_deploy#L117

Basically, in the generated tar for OSX some applications that don't directly use the frameworks style of libraries want a dylib library name. Copying those lines should do the trick