`cargo fmt` runs on `.rs` alone and `cargo doc` also on `docs/*.md`, so a docs-only commit pays the expensive hook; and the lexicon tests are not the only tests a hook runs, since `build-site.sh` and `test-publish-site.sh` both run suites of their own. Change-Id: Ibe45ea4fa1d9af4e82f248c5f59ec582fa945460