Move copy-files step to end of preprocess
Move copy-files step to end of preprocess

Per:
- https://github.com/dita-ot/dita-ot/pull/3196
- https://github.com/dita-ot/dita-ot/commit/e9afa8b

Signed-off-by: Roger Sheen <a61a1add71dadc74037ae5e44ee30713db9a7451@infotexture.net>

dita-ot/docs,infotexture/docs,infotexture/docs