update contributor name

This changes my name in the COPYRIGHT file, and adds a .mailmap entry
for my new name.

.mailmap

+Ada Worcester <oss@ada.pikhq.com> <josiahw@gmail.com>

COPYRIGHT

@@ -26,6 +26,7 @@ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 Authors/contributors include:
 
 A. Wilcox
+Ada Worcester
 Alex Dowad
 Alex Suykov
 Alexander Monakov
@@ -65,7 +66,6 @@ Jeremy Huntwork
 Jo-Philipp Wich
 Joakim Sindholt
 John Spencer
-Josiah Worcester
 Julien Ramseier
 Justin Cormack
 Kaarle Ritvanen