Work around MSVC 2014 issue with future

have to wrap std::future::valid in a lambda due to noexcept?!

include/chaiscript/dispatchkit/bootstrap_stl.hpp

@@ -574,7 +574,7 @@ namespace chaiscript
         {
           m->add(user_type<FutureType>(), type);
 
-          m->add(fun(&FutureType::valid), "valid");
+          m->add(fun<bool (const FutureType &)>([](const FutureType &t) { return t.valid(); }), "valid");
           m->add(fun(&FutureType::get), "get");
           m->add(fun(&FutureType::wait), "wait");