Fix test

```
failures:

---- test_barnes_app stdout ----
    PID TTY      STAT   TIME COMMAND
      1 ?        Rs     0:00 ps x
     14 ?        R      0:00 [start-stop-daem]


thread 'test_barnes_app' panicked at 'assertion failed: `(left contains right)`
left (unescaped):
    PID TTY      STAT   TIME COMMAND
      1 ?        Rs     0:00 ps x
     14 ?        R      0:00 [start-stop-daem]


left (escaped): `"    PID TTY      STAT   TIME COMMAND\n      1 ?        Rs     0:00 ps x\n     14 ?        R      0:00 [start-stop-daem]\n"`
right: `"agentmon_loop --path"`', buildpacks/ruby/tests/integration_test.rs:138:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

buildpacks/ruby/tests/integration_test.rs

@@ -129,7 +129,7 @@ fn test_barnes_app() {
                         ("DYNO", "web.1"),
                         ("PORT", "1234"),
                     ])
-                    .command(["ps x"]),
+                    .command(["ps ax"]),
                 |container| {
                     let log_output = container.logs_wait();
                     println!("{}", log_output.stdout);