Fixed header include problems.

include/spdlog/details/registry.h

@@ -10,16 +10,16 @@
 // If user requests a non existing logger, nullptr will be returned
 // This class is thread safe
 
+#include <spdlog/details/null_mutex.h>
+#include <spdlog/logger.h>
+#include <spdlog/async_logger.h>
+#include <spdlog/common.h>
+
 #include <string>
 #include <mutex>
 #include <unordered_map>
 #include <functional>
 
-#include "./null_mutex.h"
-#include "../logger.h"
-#include "../async_logger.h"
-#include "../common.h"
-
 namespace spdlog
 {
 namespace details