### What it does
Checks for string methods that receive a single-character
`str` as an argument, e.g., `_.split("x")`.

### Why is this bad?
Performing these methods using a `char` is faster than
using a `str`.

### Known problems
Does not catch multi-byte unicode characters.

### Example
```
_.split("x");
```

Use instead:
```
_.split('x');
```