Use gcc8 as default in CI container

yocto 2.6 uses gcc8 as it's default so make the CI
docker container use the same for compatibility

Resolves openbmc/openbmc-build-scripts#23

Change-Id: If55b17b6db8e82174016f7ff7c34533ca329285c
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
1 file changed