Update guide.html to use "language: rust" in .travis.yml

travis-ci now supports "language: rust", which eliminates the need to call rustup.sh in .travis.yml.  See http://www.reddit.com/r/rust/comments/2ecocp/travis_ci_supports_rust/ for details.
It doesn't run with `--verbose`. However we newcomers should run `cargo test` with `--verbose` on travis, I think that we should directly add `--verbose` inside travis's defaults.