title: Android - retrofit 2 - canot resolve RxJava2CallAdapterFactory
body: <p>I'm using retrofit 2 and rxjava 2 in my application. These are my gradle implementations:</p>
  
  <pre><code>implementation 'com.squareup.retrofit2:retrofit:2.4.0'
  implementation 'com.squareup.retrofit2:converter-gson:2.4.0'
  implementation 'com.squareup.retrofit2:adapter-rxjava:2.4.0'
  
  implementation 'io.reactivex.rxjava2:rxjava:2.2.1'
  implementation 'io.reactivex.rxjava2:rxandroid:2.1.0'
  </code></pre>
  
  <p>This is my API connection class: </p>
  
  <pre><code>public class ApiConnection {
    private static String BaseUrl = "http://mysites.com/";
    private static Retrofit retrofit = null;
  
    public static Retrofit getClient() {
      Gson gson = new GsonBuilder()
        .setLenient()
        .create();
  
      if (retrofit == null) {
        retrofit = new Retrofit.Builder()
          .baseUrl(BaseUrl)
          .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
          .addConverterFactory(GsonConverterFactory.create(gson))
          .build();
      }
      return retrofit;
    }
  }
  </code></pre>
  
  <p>I got an error on this line : </p>
  
  <pre><code>RxJava2CallAdapterFactory
  </code></pre>
  
  <p>This is the error:</p>
  
  <pre><code>Cannot resolve symbol 'RxJava2CallAdapterFactory
  </code></pre>
  
  <p>What is wrong with my code? </p>