Update to libgit2 d675982a153

There's been some changes to the checkout strategy, especially the
SAFE_CREATE mode, which is now the RECREATE_MISSING flag, though that
shouldn't be necessary to use in the general case.

The largest changes come from the removal of the signture from
ref-modifying functions/methods and the removal of the reflog string in
all but those directly related to moving references.

1 files changed, 0 insertions, 0 deletions

diff --git a/vendor/libgit2 b/vendor/libgit2
-Subproject 04bdd97f2b63793a8720fd19007911e946ba3c5
+Subproject d675982a15388d8c413acda139b4662062cf328