Simplify a string parsing line

This fixes a clippy warning but does even better than suggested:

```
warning: this call to `from_str_radix` can be replaced with a call to `str::parse`
   --> src/parse/response.rs:119:13
    |
119 |         |s| u16::from_str_radix(s, 10),
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `s.parse::<u16>()`
    |
    = note: `#[warn(clippy::from_str_radix_10)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#from_str_radix_10
```

src/parse/response.rs

@@ -116,7 +116,7 @@ pub fn Reply_code(input: &[u8]) -> IResult<&[u8], u16> {
             take_while_m_n(3, 3, nom::character::is_digit),
             std::str::from_utf8,
         ),
-        |s| u16::from_str_radix(s, 10),
+        str::parse,
     )(input)
 }