rustfmt to exit with an error code if the input is not formatted correctly.
It will also print any found differences.
-A minimal Travis setup could look like this:
+A minimal Travis setup could look like this (requires Rust 1.24.0 or greater):
```yaml
language: rust
before_script:
-- rustup toolchain install nightly
-- rustup component add --toolchain nightly rustfmt-preview
-- which rustfmt || cargo install --force rustfmt-nightly
+- rustup component add rustfmt-preview
script:
-- cargo +nightly fmt --all -- --write-mode=diff
+- cargo fmt --all -- --write-mode=diff
- cargo build
- cargo test
```