Update AUTHORS.md

Author: feross

AUTHORS.md

@@ -45,5 +45,6 @@
 - LI (kslrwang@gmail.com)
 - Jimmy Wärting (jimmy@warting.se)
 - Justin Kalland (justin@kalland.ch)
+- greenkeeper[bot] (23040076+greenkeeper[bot]@users.noreply.github.com)
 
 #### Generated by tools/update-authors.sh.