Removed ref from to_string_ in ansicolor sink

include/spdlog/sinks/ansicolor_sink.h

@@ -10,7 +10,6 @@
 
 #include "../details/null_mutex.h"
 #include "base_sink.h"
-#include "sink.h"
 
 namespace spdlog {
 namespace sinks {
@@ -79,7 +78,7 @@ private:
     std::array<std::string, levels_count> colors_;
     void print_ccode_(const string_view_t &color_code);
     void print_range_(const memory_buf_t &formatted, size_t start, size_t end);
-    static std::string to_string_(const string_view_t &sv);
+    static std::string to_string_(const string_view_t sv);
 };
 
 template <typename Mutex>