TestMoveToSubdir: use sort.Strings() (gosimple)

```
13:06:14 pkg/directory/directory_test.go:182:2: S1032: should use sort.Strings(...) instead of sort.Sort(sort.StringSlice(...)) (gosimple)
13:06:14 	sort.Sort(sort.StringSlice(results))
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/directory/directory_test.go

@@ -179,7 +179,7 @@ func TestMoveToSubdir(t *testing.T) {
 	for _, info := range infos {
 		results = append(results, info.Name())
 	}
-	sort.Sort(sort.StringSlice(results))
+	sort.Strings(results)
 	if !reflect.DeepEqual(filesList, results) {
 		t.Fatalf("Results after migration do not equal list of files: expected: %v, got: %v", filesList, results)
 	}