Improve Docker build process, remove --disable-segfault-error

[jordikroon]

php/doc-base#285 removed --disable-segfault-error. Dockerfile was still passing this argument resulting in a warning. Thus we should remove it as well.

Also altered Makefile to write a file hash to .docker/built instead. If we don't this warning will still pop unless we manually remove that file.

[kamil-tekiela]

I'm not familiar with Docker, so I can't review it.

[jordikroon]

I'm not familiar with Docker, so I can't review it.

No worries. Much appreciated to let me know.

[cweiske]

The CMD change is fine, but I don't like the Makefile change. make lets you add file names as dependencies to tasks, and when the file changes, it will re-run the task. Adding the Dockerfile as dependency should fix that without manually comparing hashes.

[jordikroon]

Thank you for checking @cweiske. I didn't know it was that simple. But it seems to do the trick.

[cweiske]

Thanks.