GDC 5.4.0 and 6.3.0 not available in Travis CI?

[Jeremy DeHaan via D.gnu]

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?