chromium: Update stable and dev release channels.

This introduces the following new versions:

stable: 28.0.1500.71 -> 28.0.1500.95 (builds fine, tested)
dev:    30.0.1573.2  -> 30.0.1581.2  (builds fine, tested)

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