Fix deleteAuthenticationMethodById (#552)

Author: jimmyjames

src/main/java/com/auth0/client/mgmt/UsersEntity.java

@@ -732,8 +732,7 @@ public Request<Void> deleteAuthenticationMethodById(String userId, String authen
             .build()
             .toString();
 
-        return new BaseRequest<>(this.client, tokenProvider, url, HttpMethod.DELETE, new TypeReference<Void>() {
-        });
+        return new VoidRequest(this.client, tokenProvider, url, HttpMethod.DELETE);
     }
 
     /**

src/test/java/com/auth0/client/mgmt/UsersEntityTest.java

@@ -1300,8 +1300,8 @@ public void shouldDeleteUserAuthenticationMethodById() throws Exception {
         Request<Void> request = api.users().deleteAuthenticationMethodById("1", "1");
         assertThat(request, is(notNullValue()));
 
-        server.jsonResponse(AUTHENTICATOR_METHOD_UPDATE_BY_ID, 200);
-        Void response = request.execute().getBody();
+        server.noContentResponse();
+        request.execute().getBody();
         RecordedRequest recordedRequest = server.takeRequest();
 
         assertThat(recordedRequest, hasMethodAndPath(HttpMethod.DELETE, "/api/v2/users/1/authentication-methods/1"));