Do not remove just created Docker image

[iqqmuT]

docker image prune -f command removes just created spliit2 Docker image. We probably want to keep the image.

Fixes #151

[justcallmelarry]

The command docker image prune only removes dangling images, ie images that are not tagged.
The command is there to clean up previous builds of the image, as they are no longer tagged with the latest tag

While I disagree that removing this will fix #151, I also think that running prune every time is good practice, as it also removes any other dangling images (not only for spliit).

TLDR: I would be completely OK with this removal, but I doubt that it will solve the issues