Update registry.h

include/spdlog/details/registry.h

@@ -192,7 +192,7 @@ private:
 };
 
 #ifdef SPDLOG_NO_REGISTRY_MUTEX
-#include "../details/null_mutex.h"
+#include "spdlog/details/null_mutex.h"
 using registry = registry_t<spdlog::details::null_mutex>;
 #else
 #include <mutex>
@@ -200,4 +200,4 @@ using registry = registry_t<std::mutex>;
 #endif
 
 } // namespace details
-} // namespace spdlog
\ No newline at end of file
+} // namespace spdlog