### What it does
Checks for non-octal values used to set Unix file permissions.

### Why is this bad?
They will be converted into octal, creating potentially
unintended file permissions.

### Example
```
use std::fs::OpenOptions;
use std::os::unix::fs::OpenOptionsExt;

let mut options = OpenOptions::new();
options.mode(644);
```
Use instead:
```
use std::fs::OpenOptions;
use std::os::unix::fs::OpenOptionsExt;

let mut options = OpenOptions::new();
options.mode(0o644);
```