Add protection against publishing email addresses

It's possible (like happened last release) for a contributor to
end up being an email address. Even though the address is public,
some may not wish for us to plaster it all over the place.

Fix by redacting the hostname of the email address if one shows up.

tools/contributors.pl6

@@ -98,5 +98,7 @@ sub nick-to-name($nick) {
             }
         }
     }
-    $nick ?? ( %nick-to-name{lc $nick} // $nick ) !! '<unknown>';
+    $nick
+    ?? (%nick-to-name{lc $nick} // $nick).subst(/\S+ '@' <(\S+/, '<redacted>')
+    !! '<unknown>';
 }