fix travis.yml. Installing rust mannulay is not required.
fix travis.yml. Installing rust mannulay is not required.

redtankd/rust-test,redtankd/github-test,redtankd/rust-test,redtankd/github-test,redtankd/rust-test,redtankd/rust-test,redtankd/rust-test,redtankd/github-test,redtankd/github-test,redtankd/rust-test