Update jgit to 73f8acdc5c97e068143c86765995c4fb6923ee91

This includes the following jgit changes:

003862722 LockFile: create OutputStream only when needed
  this fixes  "Too many open files" errors when
  - fetching repos with many refs [1]
  - converting from reftable back to refdir format [2]

540b29bf4 Remove ReftableNumbersNotIncreasingException

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

Change-Id: I9382497720484b7520136be94a42b716436e135e
diff --git a/modules/jgit b/modules/jgit
index 5d925ec..73f8acd 160000
--- a/modules/jgit
+++ b/modules/jgit
@@ -1 +1 @@
-Subproject commit 5d925ecbb3d0977c586f0001baf20aff12823de9
+Subproject commit 73f8acdc5c97e068143c86765995c4fb6923ee91