aging_since should be formatted using format_timestamp_seconds, not f…

…ormat_duration_seconds. (#256)

src/lib/format/nns_governance.rs

@@ -109,7 +109,7 @@ pub fn display_list_neurons(blob: &[u8]) -> AnyhowResult<String> {
             writeln!(
                 fmt,
                 "Aging since: {}",
-                format_duration_seconds(neuron.aging_since_timestamp_seconds)
+                format_timestamp_seconds(neuron.aging_since_timestamp_seconds)
             )?;
         }