Remove obsolete pumpking mention

See rakudo/rakudo@636ddcd

Author: AlexDaniel

CREDITS

@@ -251,7 +251,7 @@ E: patch@cpan.org
 
 N: Patrick R. Michaud
 U: pmichaud
-D: Perl 6 (Rakudo Perl) lead developer, pumpking
+D: Perl 6 (Rakudo Perl) lead developer
 E: pmichaud@pobox.com
 
 N: Paul Cochrane