dcache: yet another fix to datanucleus dependency

Use the release version, not the old pre-release beta with the
old name.

Target: trunk
Request: 2.7
Require-book: no
Require-notes: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5925/
(cherry picked from commit 0b8d5478f31272ca13cae1fa0ffbeaac5de471ad)
Merge pull request #158 from gbehrmann/fix/2.7/rb5925

dcache: yet another fix to datanucleus dependency