updated libgit2 to support filter streaming

ammeep · ammeep · commit 9d2ca7be0f59 · 2015-02-26T16:13:53.000-08:00
diff --git a/libgit2 b/libgit2
@@ -1 +1 @@
-Subproject commit a2012c43899e6616366b47d7741b3f035e825e84
+Subproject commit d15884ce840c7eeac54fc408fdc33e03cd01bc32
