fix Xcode compiler warning "no new line at the end of file"

include/spdlog/details/backtracer.h

@@ -43,3 +43,4 @@ public:
 #ifdef SPDLOG_HEADER_ONLY
 #include "backtracer-inl.h"
 #endif
+

include/spdlog/details/synchronous_factory.h

@@ -22,3 +22,4 @@ struct synchronous_factory
     }
 };
 } // namespace spdlog
+

include/spdlog/fmt/fmt.h

@@ -25,3 +25,4 @@
 #include <fmt/core.h>
 #include <fmt/format.h>
 #endif
+

include/spdlog/sinks/basic_file_sink.h

@@ -56,3 +56,4 @@ inline std::shared_ptr<logger> basic_logger_st(const std::string &logger_name, c
 #ifdef SPDLOG_HEADER_ONLY
 #include "basic_file_sink-inl.h"
 #endif
+