Cleanup transitive includes in beast/core/detail/type_traits.hpp

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

include/boost/beast/http/impl/write.hpp

@@ -16,6 +16,7 @@
 #include <boost/beast/core/buffers_range.hpp>
 #include <boost/beast/core/make_printable.hpp>
 #include <boost/beast/core/stream_traits.hpp>
+#include <boost/beast/core/detail/is_invocable.hpp>
 #include <boost/asio/coroutine.hpp>
 #include <boost/asio/post.hpp>
 #include <boost/asio/write.hpp>