travis: Build aspeed board with qemu HEAD

In order to boot u-boot in the aspeed machine we need to run at least
qemu 3059c2f5a813 (v4.0.0-1592-g3059c2f5a813), which is not in a
released tag.

This should be changed to v4.1.0 when it is released.

Signed-off-by: Joel Stanley <joel@jms.id.au>