Add 'Send' bound for PackedClient client future.

The Future is Send anyway, but this bound on the Box is neccessary
to use the future across threads because the compiler can't figure
out the Send bound otherwise.

src/client/mod.rs

@@ -828,7 +828,7 @@ impl Future for IrcClientFuture {
 /// This type should only be used by advanced users who are familiar with the implementation of this
 /// crate. An easy to use abstraction that does not require this knowledge is available via
 /// [`IrcReactors`](./reactor/struct.IrcReactor.html).
-pub struct PackedIrcClient(pub IrcClient, pub Box<Future<Item = (), Error = error::IrcError>>);
+pub struct PackedIrcClient(pub IrcClient, pub Box<Future<Item = (), Error = error::IrcError> + Send>);
 
 #[cfg(test)]
 mod test {