Add JGit upgrade in 2.15 release notes

Change-Id: Ief75b71782aa85c52a6ee39264cb28707ca04401
diff --git a/releases/2.15.md b/releases/2.15.md
index f30a4eb..e8a6608 100644
--- a/releases/2.15.md
+++ b/releases/2.15.md
@@ -267,6 +267,8 @@
 
 * Update Jetty to 9.3.18.v20170406
 
+* Update JGit to 4.9.0.201710071750-r
+
 * Update Joda-Time to 2.9.9
 
 * Update juniversalchardet to 2.0.0