Ensure image sprawl is avoided miscalculation

[halfluke]

[INFO] 6 - Docker Security Operations
[INFO] 6.1 - Ensure that image sprawl is avoided (Manual)
[INFO] * There are currently: 14 images
[INFO] * Only 0 out of 14 are in use

fix: change
for c in $(docker inspect --format "{{.Image}}" "$(docker ps -qa)" 2>/dev/null); do
to
for c in $(docker inspect --format "{{.Image}}" $(docker ps -qa) 2>/dev/null); do

The first command returns an error for the first image and the whole count fails

[konstruktoid]

Hi @halfluke and thanks for find this issue.

Could you submit a PR?