title: requestFactory(Class<? extends ClientHttpRequestFactory>) in the type RestTemplateBuilder is not applicable
body: <p>I am using springBootVersion = '2.0.1.RELEASE' on my project. I am trying to write mutual authentication code for that I wrote RestClientCertTestConfiguration class as below. I am getting error on requestFactory. 
  The method requestFactory(Class) in the type RestTemplateBuilder is not applicable for the arguments (HttpComponentsClientHttpRequestFactory)
  Any suggestion on how to resolve this issue? thanks</p>
  
  <pre><code>    @Configuration
  public class RestClientCertTestConfiguration {
  
      private String allPassword = "mypassword";
  
      @Bean
      public RestTemplate restTemplate(RestTemplateBuilder builder) throws Exception {
  
          SSLContext sslContext = SSLContextBuilder
                  .create()
                  .loadKeyMaterial(ResourceUtils.getFile("classpath:myCerts.jks"), allPassword.toCharArray(), allPassword.toCharArray())
                  .loadTrustMaterial(ResourceUtils.getFile("classpath:myCerts.jks"), allPassword.toCharArray())
                  .build();
  
          HttpClient client = HttpClients.custom()
                  .setSSLContext(sslContext)
                  .build();
  
          return builder 
                   //error on this line
                  .requestFactory(new HttpComponentsClientHttpRequestFactory(client))
                  .build();
      }
  
  }
  </code></pre>