It was actually disk space, which makes me think your package must be well over 4Gb. In any case, we increased your disk size by 10Gb.
But as an additional precautionary step, you can try to remove things on the VM that you are not using but that are taking a lot of that space. Cygwin alone, for instance, if removed can allow you to reclaim a few GB of space.
Just add these two lines to the init: stage of your yaml config file.
The cleaning process takes more than 13 minutes, so I would assume it frees a lot of disk space. But even like this, I could not make my build pass. It fails really close to the end: sometimes my artefacts are deployed via my custom deploy_script, but even then the build still fails with the same error message:
Build exceeded allowed resource quotas. Fix your build to consume less resources or contact AppVeyor support to request quotas increase.
I am not sure what resource quota I am exceeding here. Locally, my build does not appear to ask that much resource. Any hint on how I can figure out what resource is lacking (disk space, memory, ...) and how I can solve it?