Restore compatibility with rust 1.31

    error: cannot find macro `matches!` in this scope
        --> src/lit.rs:1121:32
         |
    1121 |                             if matches!(b, b' ' | b'\t' | b'\n' | b'\r') {
         |                                ^^^^^^^

src/lit.rs

@@ -1118,10 +1118,9 @@ mod value {
                         b'"' => '"',
                         b'\r' | b'\n' => loop {
                             let b = byte(s, 0);
-                            if matches!(b, b' ' | b'\t' | b'\n' | b'\r') {
-                                s = &s[1..];
-                            } else {
-                                continue 'outer;
+                            match b {
+                                b' ' | b'\t' | b'\n' | b'\r' => s = &s[1..],
+                                _ => continue 'outer,
                             }
                         },
                         b => panic!("unexpected byte {:?} after \\ character in byte literal", b),