Fix shellcheck warning

JohnTitor · JohnTitor · commit b52e8e00f477 · 2020-03-05T03:26:55.000+09:00
diff --git a/ci/style.sh b/ci/style.sh
@@ -5,7 +5,7 @@ set -ex
 rustc ci/style.rs && ./style src
 
 if rustup component add rustfmt-preview ; then
-    which rustfmt
+    command -v rustfmt
     rustfmt -V
     cargo fmt --all -- --check
 fi
