Add cargo fmt to travis build config

.travis.yml

@@ -4,3 +4,8 @@ rust:
     - stable
     - beta
     - nightly
+
+script:
+  - if [[ "$TRAVIS_RUST_VERSION" == *stable* ]]; then rustup component add rustfmt; cargo fmt --version; cargo fmt -- --check || (echo "Please reformat your code with 'cargo fmt' (version $(cargo fmt --version))"; false); fi
+  - cargo build -v
+  - cargo test -v