Include git2/transaction.h This was forgotten when the feature was implemented.
diff --git a/include/git2.h b/include/git2.h
index cf6b5cb..d141c59 100644
--- a/include/git2.h
+++ b/include/git2.h
@@ -58,6 +58,7 @@
#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"