Hi, sorry for the late answer:
Generally speaking: you want to use a released version of the LITIENGINE. The Gurk Nukem project directly references the LITIENGINE as a project. This is not the recommended way of doing things but since the game is used as a sample project for the engine, and thereby always kept up to date, we decided to use that setup.
As an end-user of the engine, you should use a released version of it. This has been previously discussed in this GitHub issue
In short: use
compile 'de.gurkenlabs:litiengine:0.5.0 instead of
compile project(':litiengine') in your
We should probably adjust the sample project to that format because it's not making the intended usage very clear.
Thank you for your feedback/question.