Fix example

example/example.cpp

@@ -119,9 +119,9 @@ void callback_example() {
 
 #include "spdlog/sinks/async_sink.h"
 void async_example() {
-    auto logger = spdlog::create_async("some_logger");
-    auto file_sink = std::make_shared<basic_file_sink_mt>("logs/async_log.txt", true);
-    logger->sinks().push_back(file_sink);
+    using spdlog::sinks::async_sink;
+    auto sink = async_sink::with_sink<basic_file_sink_mt>("logs/async_log.txt", true);
+    auto logger = std::make_shared<spdlog::logger>("async_logger", sink);
     for (int i = 1; i < 101; ++i) {
         logger->info("Async message #{}", i);
     }