### What it does
Checks for implicit saturating subtraction.

### Why is this bad?
Simplicity and readability. Instead we can easily use an builtin function.

### Example
```
let mut i: u32 = end - start;

if i != 0 {
    i -= 1;
}
```

Use instead:
```
let mut i: u32 = end - start;

i = i.saturating_sub(1);
```