build and lint the UI in travis-ci

This is a separate item in the matrix, so it doesn't go through this for
each of the three Rust versions.

ci/script-rust.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -e
+cargo build --all
+cargo test --all
+if [ "$TRAVIS_RUST_VERSION" = nightly ]; then
+  cargo bench --all
+fi