Hi there! We have a DRM-free version of the current build for our backers, but we highly encourage to get the Steam version since the game is still being developed. We'll add a DRM-free version after the full release.
Since you bought it through Humble Bundle (and the same would apply to everyone who bought it through itchio), we can add the DRM-free version to the package, so you'll be able to get it if you look at your purchases, without any additional cost.