increase err clarity when testing from stdin and fix windows integration test

Author: dylanhitt

commander_windows.yaml

@@ -65,7 +65,7 @@ tests:
     exit-code: 1
 
   test retries with stdin:
-    command: cat integration/windows/retries.yaml | commander.exe test -
+    command: type integration/windows/retries.yaml | commander.exe test -
     stdout:
       contains:
         - ✗ [local] echo hello, retries 3

pkg/app/test_command.go

@@ -133,7 +133,7 @@ func testStdin(filters runtime.Filters) (runtime.Result, error) {
 	}
 
 	if f.Mode()&os.ModeCharDevice != 0 {
-		return runtime.Result{}, fmt.Errorf("Error: command is intended to work with pipes")
+		return runtime.Result{}, fmt.Errorf("Error: when testing from stdin the command is intended to work with pipes")
 	}
 
 	r := bufio.NewReader(os.Stdin)