Fix includes of list/min_element.hpp

Author: ecrypa

include/metal/list/min_element.hpp

@@ -5,6 +5,7 @@
 #include "../lambda/apply.hpp"
 #include "../lambda/lambda.hpp"
 #include "../list/list.hpp"
+#include "../number/if.hpp"
 #include "../value/fold_left_v2.hpp"
 
 namespace metal {