Fix rest::send_file
Fix rest::send_file

Remove usage of `Value::to_string` - which would encapsulate the
produced value with quotation marks - and instead match the type of
value and wwrite the text accordingly.

Roughsketch/serenity,Lakelezz/serenity,zeyla/serenity.rs,acdenisSK/serenity,eLunate/serenity,Flat/serenity,zeyla/serenity