fix include optional on alpine 3.7

agui2/src/Converter.hpp

 #pragma once
 #include <tuple>
-#include <optional>
+
+#if __has_include(<optional>) && __cplusplus >= 201703L //FIXME has_include to allow build on gitlab-ci with alpine 3.7
+	#include <optional>
+#else
+	#include <experimental/optional>
+	namespace std {
+		template < class T >
+		using optional = experimental::optional < T >;
+
+		constexpr auto nullopt = std::experimental::nullopt;
+	}
+#endif
 #include <QString>
 #include <QImage>