I've updated a Travis CI script to test my project against the new 2.068.2 GDC versions, but 5.4.0 and 6.3.0 don't seem to be available. When Travis runs, I get a `Failed to download 'http://gdcproject.org/downloads/binaries/x86_64-linux-gnu/gdc-5.4.0.tar.xz'` error (or similar). Any idea what's going on here?