Ignore needless_doctest_main clippy lint

warning: needless `fn main` in doctest
      --> src/lib.rs:22:5
       |
    22 |   //! fn main() {
       |  _____^
    23 | | //!     let mut buffer = itoa::Buffer::new();
    24 | | //!     let printed = buffer.format(128u64);
    25 | | //!     assert_eq!(printed, "128");
    26 | | //! }
       | |_____^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_doctest_main
       = note: `-W clippy::needless-doctest-main` implied by `-W clippy::all`
       = help: to override `-W clippy::all` add `#[allow(clippy::needless_doctest_main)]`

src/lib.rs

@@ -37,6 +37,7 @@
     clippy::cast_possible_truncation,
     clippy::expl_impl_clone_on_copy,
     clippy::must_use_candidate,
+    clippy::needless_doctest_main,
     clippy::unreadable_literal
 )]