nit: fix comment in test (#1418)

Author: zhiqiangxu

actors/miner/tests/declare_recoveries.rs

@@ -63,7 +63,7 @@ fn recovery_must_pay_back_fee_debt() {
     st = h.get_state(&rt);
     let (dl_idx, p_idx) = st.find_sector(&rt.store, one_sector[0].sector_number).unwrap();
 
-    // Skip to end of proving period
+    // advance into the deadline but not past it
     h.advance_to_deadline(&rt, dl_idx);
 
     // Can't pay during this deadline so miner goes into fee debt