#14472: Update .gitignore

Patch by Matej Cepl.
diff --git a/Misc/ACKS b/Misc/ACKS
index d5a3510..265cb17 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -161,6 +161,7 @@
 Donn Cave
 Charles Cazabon
 Per Cederqvist
+Matej Cepl
 Octavian Cerna
 Pascal Chambon
 John Chandler