Update libgit2 source code (013924)

* Update libgit2 source code to commit
  013924c17c03c42bce363ea1ddc949444164c2bc

Signed-off-by: Stefan Widgren <stefan.widgren@gmail.com>
Handle changes in libgit2 API

* src/git2r_note.c (git2r_note_create): libgit2 has changed the
  position of the notes reference name in git_note_create.

Signed-off-by: Stefan Widgren <stefan.widgren@gmail.com>