Forbid clippy warnings

ci/script.sh

@@ -5,7 +5,7 @@ set -ex
 # TODO This is the "test phase", tweak it as you see fit
 main() {
     cargo fmt --all -- --check
-    cargo clippy --all-targets --all-features -- -D warnings
+    cargo clippy --all-targets --all-features
     cross check --target $TARGET
     cross check --target $TARGET --release
 

src/main.rs

@@ -1,3 +1,5 @@
+#![cfg_attr(feature = "cargo-clippy", deny(clippy::all))]
+
 extern crate directories;
 extern crate failure;
 extern crate which;