Fix broken images API for version <1.7

Simple typo, "ID" should be "Id".  This is causing the images response
to not have IDs in it.

Docker-DCO-1.1-Signed-off-by: Darren Shepherd <darren.s.shepherd@gmail.com> (github: ibuildthecloud)
Merge pull request #3954 from ibuildthecloud/broken-1.6-images-api

Fix broken images API for version <1.7