[PATCH 1/2] .travis: Use source whitelist alias for llvm-6 repository

Fixes issue with unauthenticated packages.
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

a successful build can be seen here:

Jan

These 2 look ok to me.

--Aaron

thank you.
I pushed all 3.

Jan