### What it does
Checks for ranges which almost include the entire range of letters from 'a' to 'z', but
don't because they're a half open range.

### Why is this bad?
This (`'a'..'z'`) is almost certainly a typo meant to include all letters.

### Example
```
let _ = 'a'..'z';
```
Use instead:
```
let _ = 'a'..='z';
```