travis: These builds no longer fail.
travis: These builds no longer fail.

The Xilinx toolchain has been fixed so these builds no longer fail. \o/

Fixes https://github.com/timvideos/HDMI2USB-litex-firmware/issues/455

mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware