Add missing include to scanscalar.cpp

src/scanscalar.cpp

+#include "scanscalar.h"
+
+#include <algorithm>
+
 #include "exp.h"
 #include "regeximpl.h"
-#include "scanscalar.h"
 #include "stream.h"
 #include "yaml-cpp/exceptions.h"  // IWYU pragma: keep