Update webfinger and reqwest

Update webfinger to 0.3.1
Update reqwest to 0.9
Fix #257

plume-common/src/activity_pub/mod.rs

@@ -104,11 +104,11 @@ pub fn broadcast<S: sign::Signer, A: Activity, T: inbox::WithInbox + Actor>(send
     for inbox in boxes {
         // TODO: run it in Sidekiq or something like that
         let mut headers = request::headers();
-        headers.set(request::Digest::digest(signed.to_string()));
+        headers.insert("Digest", request::Digest::digest(signed.to_string()));
         let res = Client::new()
             .post(&inbox[..])
             .headers(headers.clone())
-            .header(request::signature(sender, headers))
+            .header("Signature", request::signature(sender, headers))
             .body(signed.to_string())
             .send();
         match res {