update contributor name

This changes my name in the COPYRIGHT file, and adds a .mailmap entry
for my new name.
diff --git a/COPYRIGHT b/COPYRIGHT
index 67802d1..0350109 100644
--- a/COPYRIGHT
+++ b/COPYRIGHT
@@ -26,6 +26,7 @@
 Authors/contributors include:
 
 A. Wilcox
+Ada Worcester
 Alex Dowad
 Alex Suykov
 Alexander Monakov
@@ -65,7 +66,6 @@
 Jo-Philipp Wich
 Joakim Sindholt
 John Spencer
-Josiah Worcester
 Julien Ramseier
 Justin Cormack
 Kaarle Ritvanen