Resolve ignored_unit_patterns pedantic clippy lint

    warning: matching over `()` is more explicit
        --> src/de.rs:2409:59
         |
    2409 | ...                   self.peek_end_of_value().map(|_| value)
         |                                                     ^ help: use `()` instead of `_`: `()`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ignored_unit_patterns
         = note: `-W clippy::ignored-unit-patterns` implied by `-W clippy::pedantic`

Author: dtolnay

src/de.rs

@@ -2406,7 +2406,7 @@ where
                         if self_delineated_value {
                             Ok(value)
                         } else {
-                            self.peek_end_of_value().map(|_| value)
+                            self.peek_end_of_value().map(|()| value)
                         }
                     }
                     Err(e) => {