Update ChangeLog for 4.2.0.
diff --git a/ChangeLog b/ChangeLog
index a939094..926209e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,7 +4,7 @@
 
     https://github.com/jemalloc/jemalloc
 
-* 4.2.0 (XXX)
+* 4.2.0 (May 12, 2016)
 
   New features:
   - Add the arena.<i>.reset mallctl, which makes it possible to discard all of