Ignore new_without_default clippy lint

    error: you should consider adding a `Default` implementation for `UnitDeserializer<E>`
       --> serde/src/de/value.rs:144:5
        |
    144 | /     pub fn new() -> Self {
    145 | |         UnitDeserializer {
    146 | |             marker: PhantomData,
    147 | |         }
    148 | |     }
        | |_____^
        |
        = note: `-D clippy::new-without-default` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#new_without_default
    help: try adding this
        |
    142 + impl<E> Default for UnitDeserializer<E> {
    143 +     fn default() -> Self {
    144 +         Self::new()
    145 +     }
    146 + }
        |

serde/src/lib.rs

@@ -123,6 +123,7 @@
         explicit_auto_deref,
         let_underscore_drop,
         map_err_ignore,
+        new_without_default,
         result_unit_err,
         wildcard_imports,
         // not practical