Add missing <chrono> include in Playlist.cpp

Author: kblaschke

src/playlist/Playlist.cpp

@@ -1,6 +1,7 @@
 #include "Playlist.hpp"
 
 #include <algorithm>
+#include <chrono>
 
 // Fall back to boost if compiler doesn't support C++17
 #include PROJECTM_FILESYSTEM_INCLUDE