Ignore clone_instead_of_copied pedantic clippy lint

Iterator::copied was introduced in Rust 1.35, whereas serde_test
currently supports a minimum compiler version of 1.13.

    error: used `cloned` where `copied` could be used instead
       --> serde_test/src/de.rs:49:29
        |
    49  |         self.tokens.first().cloned()
        |                             ^^^^^^ help: try: `copied`
        |
    note: the lint level is defined here
       --> serde_test/src/lib.rs:149:52
        |
    149 | #![cfg_attr(feature = "cargo-clippy", deny(clippy, clippy_pedantic))]
        |                                                    ^^^^^^^^^^^^^^^
        = note: `#[deny(clippy::cloned_instead_of_copied)]` implied by `#[deny(clippy::pedantic)]`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cloned_instead_of_copied

serde_test/src/lib.rs

@@ -153,6 +153,7 @@
 #![cfg_attr(
     feature = "cargo-clippy",
     allow(
+        cloned_instead_of_copied,
         empty_line_after_outer_attr,
         missing_docs_in_private_items,
         missing_panics_doc,