travis: SWR requires LLVM 6.0

v2: update clarification why ubuntu-toolchain-r-test is required (Emil)

Fixes: 0cef0cccf51 ("swr: bump minimum supported LLVM version to 6.0")
Cc: Dylan Baker <dylan@pnwbakers.com>
Cc: Eric Engestrom <eric.engestrom@intel.com>
Acked-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
1 file changed