git: update to v2.7.0

Update to git version v2.7.0.

* Upstream commit ed1c9977cb1b63e4270ad8bdf967a2d02580aa08 (Remove
  get_object_hash.) changed API:

  Convert all instances of get_object_hash to use an appropriate
  reference to the hash member of the oid member of struct object.
  This provides no functional change, as it is essentially a macro
  substitution.

Signed-off-by: Christian Hesse <mail@eworm.de>

shared.c

@@ -402,8 +402,8 @@ void cgit_diff_commit(struct commit *commit, filepair_fn fn, const char *prefix)
 	unsigned char *old_sha1 = NULL;
 
 	if (commit->parents)
-		old_sha1 = commit->parents->item->object.sha1;
-	cgit_diff_tree(old_sha1, commit->object.sha1, fn, prefix,
+		old_sha1 = commit->parents->item->object.oid.hash;
+	cgit_diff_tree(old_sha1, commit->object.oid.hash, fn, prefix,
 		       ctx.qry.ignorews);
 }