use Sleep in Windows instead of sleep_for

fixes #609

include/spdlog/details/os.h

@@ -362,6 +362,15 @@ inline size_t thread_id()
 
 }
 
+// from https://github.com/gabime/spdlog/issues/609
+inline void sleep_for_millis(int milliseconds)
+{
+#if defined(_WIN32)
+    Sleep(milliseconds);
+#else
+    std::this_thread::sleep_for(std::chrono::milliseconds(milliseconds));
+#endif
+}
 
 // wchar support for windows file names (SPDLOG_WCHAR_FILENAMES must be defined)
 #if defined(_WIN32) && defined(SPDLOG_WCHAR_FILENAMES)