fix compilation warnings
fix compilation warnings

Summary: Closes https://github.com/ReactiveSocket/reactivesocket-cpp/pull/317

Differential Revision: D4661210

Pulled By: lehecka

fbshipit-source-id: 5b8314bb9c83372494aba9c11078915f8efc909b

phoad/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,vjn/reactivesocket-cpp,alexmalyshev/rsocket-cpp,phoad/rsocket-cpp,vjn/rsocket-cpp,phoad/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,vjn/reactivesocket-cpp,ReactiveSocket/reactivesocket-cpp,alexmalyshev/rsocket-cpp,phoad/rsocket-cpp,rsocket/rsocket-cpp,vjn/reactivesocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp,alexmalyshev/rsocket-cpp,vjn/rsocket-cpp,phoad/rsocket-cpp,vjn/rsocket-cpp,rsocket/rsocket-cpp,alexmalyshev/rsocket-cpp