Automate code formatting check on CI

Author: no111u3

ci/install.sh

@@ -4,6 +4,7 @@ main() {
     if [ $TARGET != x86_64-unknown-linux-gnu ]; then
         rustup target add $TARGET
     fi
+    rustup component add rustfmt
 }
 
 main

ci/script.sh

@@ -3,6 +3,7 @@ set -euxo pipefail
 main() {
     cargo check --target $TARGET
     cargo check --target $TARGET --features unproven
+    cargo fmt -- --check
 
     if [ $TRAVIS_RUST_VERSION = nightly ]; then
         cargo test --target $TARGET --features unproven