Update jgit to a9579ba60cd2fd72179dfd8c2c37d389db5ec402

This version fixes  "Too many open files" errors when
- fetching repos with many refs [1]
- converting from reftable back to refdir format [2]

[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=552173
[2] https://bugs.eclipse.org/bugs/show_bug.cgi?id=573328

Change-Id: Id3a4adc0faf27e7bcd2017ab439aa2230cf92b33
diff --git a/modules/jgit b/modules/jgit
index c82818e..a9579ba 160000
--- a/modules/jgit
+++ b/modules/jgit
@@ -1 +1 @@
-Subproject commit c82818e0e02a9d1bd979d27bd342bb05661150d4
+Subproject commit a9579ba60cd2fd72179dfd8c2c37d389db5ec402