git: update to v2.13.4

Update to git version v2.13.4: With commit 8aee769f (pathspec: copy and free
owned memory) the definition of struct pathspec_item has changed with the
expectation that pathspecs will be managed dynamically. We work around this
a bit by setting up a static structure, but let's allocate the match string
to avoid needing to cast away const.

Updated a patch from John Keeping <john@keeping.me.uk> for git v2.12.1.

1 files changed, 0 insertions, 0 deletions

diff --git a/git b/git
-Subproject 454cb6bd52a4de614a3633e4f547af03d5c3b64
+Subproject cf8899d285d2648013040ec7196ffd3de060666