anki: Fix hash of the source tarball

Searching the web for the base-16 encoded hash of the one we have in the
Nix expression didn't give any results and I also couldn't find the
older tarball anywhere (even the mirrors I've checked don't have it).

So checking the updated hash I've found that other distros use this, so
I'd bet it's safe to do this.

I've tested building the package but I didn't do any runtime test.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @the-kenny