Update version to 2014-09-29b

This update contains security fixes, see the full list of changes here:
https://www.dokuwiki.org/changes#release_2014-09-29b_hrun

It seems github changed the codeload url schema for tar.gz, they removed
the 'legacy' part. I changed the path so now it works.

Furthermore, `codeload.github.com` doesn't seem documented anywhere so they can break again anytime. We should consider to use the redirect url directly with the `-L` (follow redirects) curl option: https://github.com/splitbrain/dokuwiki/archive/release_stable_2014_09_29b.tar.gz