Update .travis.yml

[volzkzg]

In case you can not find the option --check

[davidalber]

Hi @volzkzg. Thanks for your contribution!

The purpose of this repository is to verify the example Travis CI config in rustfmt's README works. Thus, the .travis.yml file here is expected to match the snippet in the rustfmt snippet. I would be happy to merge your changes if they are first merged to rustfmt.

The build for this change still failed on the --check flag.

$ rustup component add rustfmt-preview
$ rustup self update
$ cargo fmt --all -- --check
Unrecognized option: 'check'

The command "cargo fmt --all -- --check" exited with 1.

[volzkzg]

@davidalber Hi David, I solved the problem Unrecognized option: check by add the line

rustup self update

in my case. That's why I made this contribution when I saw you have the same problem.

Let me check what's the real problem here.

[davidalber]

I believe it's because you are using nightly.

[volzkzg]

Yeah, that's true. So I guess it will be solved when next stable version releases.

[davidalber]

👍 In rust-lang/rustfmt#2688, I asked when that will happen.