Normalize server from group actor too

as specified in tests

src/utils.rs

@@ -19,8 +19,8 @@ impl<V, E: Error> LogError for Result<V, E> {
     }
 }
 
-pub(crate) fn acct_to_server(acct: &str) -> Option<&str> {
-    acct.trim_start_matches('@').split('@').nth(1)
+pub(crate) fn acct_to_server(acct: &str) -> Option<String> {
+    acct.trim_start_matches('@').split('@').nth(1).map(|s| s.to_lowercase())
 }
 
 pub(crate) fn normalize_acct(acct: &str, group: &str) -> Result<String, GroupError> {
@@ -45,8 +45,8 @@ mod test {
 
     #[test]
     fn test_acct_to_server() {
-        assert_eq!(Some("novak"), acct_to_server("pepa@novak"));
-        assert_eq!(Some("banana.co.uk"), acct_to_server("@pepa@banana.co.uk"));
+        assert_eq!(Some("novak".to_string()), acct_to_server("pepa@novak"));
+        assert_eq!(Some("banana.co.uk".to_string()), acct_to_server("@pepa@banana.co.uk"));
         assert_eq!(None, acct_to_server("probably_local"));
     }