Check formatting and clippy on CI builds

.travis.yml

@@ -1,11 +1,16 @@
 language: rust
 rust:
+  - 1.31.0
   - stable
   - beta
   - nightly
 matrix:
   allow_failures:
     - rust: nightly
+before_script:
+  - rustup component add clippy
+  - rustup component add rustfmt
+script: ci/script.sh
 after_success:
   - if [ "$TRAVIS_RUST_VERSION" == "nightly" ]; then
         cargo bench;

ci/script.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+set -ex
+
+cargo build
+cargo test
+
+# On Rust 1.31.0, we only care about passing tests.
+if [ ! rustc --version | grep "^rustc 1.31.0" ]; then
+  cargo fmt --all -- --check
+  cargo clippy -- -D warnings
+fi
+
+