Include git2/transaction.h This was forgotten when the feature was implemented.
diff --git a/include/git2.h b/include/git2.h
index a1e7837..ac4a631 100644
--- a/include/git2.h
+++ b/include/git2.h
@@ -57,6 +57,7 @@
#include "git2/submodule.h"
#include "git2/tag.h"
#include "git2/transport.h"
+#include "git2/transaction.h"
#include "git2/tree.h"
#include "git2/types.h"
#include "git2/version.h"