fix(macos): load zlib

[gmurayama]

Latest version of Pitaya fails on Unity Editor running on Mac OS

DllNotFoundException: libpitaya-mac assembly:<unknown assembly> type:<unknown type> member:(null)
Pitaya.StaticPitayaBinding.SetLogFunction (NativeLogFunction fn) (at <b477b557aa9a4327aaf49e545dc992f2>:0)
Pitaya.StaticPitayaBinding..cctor () (at <b477b557aa9a4327aaf49e545dc992f2>:0)
Rethrow as TypeInitializationException: The type initializer for 'Pitaya.StaticPitayaBinding' threw an exception.
Pitaya.PitayaBinding.set_QueueDispatcher (Pitaya.IPitayaQueueDispatcher value) (at <b477b557aa9a4327aaf49e545dc992f2>:0)

The root cause is a failure in loading zlib. The fix add a fallback path to /usr/lib in order to find the shared lib libz.1.dylib