Fix test-notify for systems without or with a different version of diffstat.
Some diffstat versions say "1 file changed", others "1 files changed".
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b