Relax image_optim dependency

Make it depend on the last minor version, rather than revision.

Change-Id: Ief6540676eb1aad58ff45d6c2354f68bb8f9e88e
Reviewed-on: http://gerrit.causes.com/37008
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>