Resolve sliced_string_as_bytes clippy lint

    warning: calling `as_bytes` after slicing a string
        --> src/lit.rs:1540:21
         |
    1540 |         let mut v = s[2..].as_bytes();
         |                     ^^^^^^^^^^^^^^^^^ help: try: `&s.as_bytes()[2..]`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#sliced_string_as_bytes
         = note: `-W clippy::sliced-string-as-bytes` implied by `-W clippy::all`
         = help: to override `-W clippy::all` add `#[allow(clippy::sliced_string_as_bytes)]`

src/lit.rs

@@ -1537,7 +1537,7 @@ mod value {
         assert_eq!(byte(s, 1), b'\'');
 
         // We're going to want to have slices which don't respect codepoint boundaries.
-        let mut v = s[2..].as_bytes();
+        let mut v = &s.as_bytes()[2..];
 
         let b = match byte(v, 0) {
             b'\\' => {