Require i18n =0.6.9 because 0.6.11 is broken.

Hi Matthew,
Can you guys test this?

Rest of commit message:

If you've built the tarball (make tarball) before this update, you might need to clear out some stuff:

  rm -r vendor/*
  rm -r build/*
  rm tools/*.lock

See
* https://github.com/svenfuchs/i18n/issues/270