I’m guessing that that’s just a temporary DNS failure on the build server. I would say you should have them re-run it, but when I tried building it with fdroid I get the following error:
/home/tom/repositories/fdroiddata/build/com.numguesser.tonio_rpchp.numberguesser/app/src/main/java/com/numguesser/tonio_rpchp/numberguesser/Guesser.java:152: error: cannot find symbol
symbol: variable android_genio_o
location: class drawable
FAILURE: Build failed with an exception.
When I check the source, I see that android_genio.png is not defined for all resolutions, so that’s probably the cause. I think you could put the image in /drawable/ (with no resolution specified) and have it work.