Does not compile on 1.15 (nightly)

[jjuraszek]

https://travis-ci.org/serde-rs/serde/jobs/176255470

[dtolnay]

Thanks for the report! The three things broken in that build are Clippy and two Rust issues:

• https://github.com/Manishearth/rust-clippy/issues/1343
• Compilation on Ubuntu 12.04 no longer succeeds rust-lang/rust#37786
• ICE using new attributes(..) section of #[proc_macro_derive] rust-lang/rust#37788

I see progress already on all of those so I don't think there is any action here for Serde.