Images not regenerating if cache present #93

My understanding is that if I run

python -m checkit generate --outcome TR1-100 --regenerate --images

The images should always regenerate. However, in 0.2.8b1 it seems if there is some cache present (not 100% sure on what reliably causes this behavior) this is not happening. I can force it to regenerate by adding or removing a blank line in the generator file---I suspect it is hashing this file and comparing the hashes, and only regenerating images if a different hash is present. However, I think it should respect the --images and regenerate images.