add notes for failing util.format test cases due to https://github.com/tessel/runtime/issues/292, https://github.com/tessel/runtime/issues/294, https://github.com/tessel/runtime/issues/295, https://github.com/tessel/runtime/issues/296, https://github.com/tessel/runtime/issues/298, https://github.com/tessel/runtime/issues/299
travisplexer: pr-291-linux travis ci test