JakeWharton Update to OkHttp 3.11
Use get instead of parse for HttpUrl and MediaType where valid input is always required.
Latest commit ce71d05 Jul 13, 2018

README.md

Retrofit Adapters

Retrofit ships with a default adapter for executing Call instances. The child modules contained herein are additional adapters for other popular execution mechanisms.

To use, supply an instance of your desired adapter when building your Retrofit instance.

Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("https://api.example.com")
    .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
    .build();