Enforce cargo fmt in Travis

Closes #198.

Author: tmandry

.travis.yml

@@ -3,8 +3,11 @@ rust:
   - beta
   - nightly
 script:
+  # RUSTC_BOOTSTRAP enables e.g. #![feature] on beta
+  - rustup component add rustfmt
   - cd chalk-engine && RUSTC_BOOTSTRAP=1 cargo build --no-default-features && cd ..
   - cd chalk-engine && RUSTC_BOOTSTRAP=1 cargo build --all-features && cd ..
+  - cargo fmt --all -- --check
   - RUSTC_BOOTSTRAP=1 cargo test --all
   - RUSTC_BOOTSTRAP=1 cargo doc --all --document-private-items
 deploy: