chromium: Fix omahaproxy URL in updater.

Omahaproxy got an overhaul and thus doesn't give CSV output on the main URL
anymoare. We're switching to /all for now and may want to refine this to only
what we're exactly looking for, but for now it fixes the updater.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>