mark 5.25.1 release as done

Author: xsawyerx

Porting/release_schedule.pod

@@ -49,7 +49,7 @@ you should reset the version numbers to the next blead series.
 =head2 Perl 5.25
 
   2016-04-08  5.25.0 ✓        Ricardo Signes
-  2016-05-20  5.25.1          Sawyer X
+  2016-05-20  5.25.1 ✓        Sawyer X
   2016-06-20  5.25.2          Matthew Horsfall
   2016-07-20  5.25.3          Steve Hay
   2016-08-20  5.25.4          BinGOs