Avoid using clap deprecated features (#787)

The PR will fix #786 .

In order to minimize future security risks and maintain ease of use, it
is recommended to avoid using deprecated features of clap.

I have refactored the code so that no warning appears when the following
command is executed:

```sh
cargo check --features clap/deprecated
```

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/integration.rs b/tests/integration.rs
index 3774792..c2d9cca 100644
--- a/tests/integration.rs
+++ b/tests/integration.rs
@@ -769,3 +769,16 @@ fn test_all_directory() {
         .assert()
         .stdout(predicate::str::is_match(".").unwrap());
 }
+
+#[test]
+fn test_multiple_files() {
+    let dir = tempdir();
+    dir.child("one").touch().unwrap();
+    dir.child("two").touch().unwrap();
+
+    cmd()
+        .arg(dir.path().join("one"))
+        .arg(dir.path().join("two"))
+        .assert()
+        .stdout(predicate::str::is_match(".").unwrap());
+}