replace serde_macros by serde_derive

[little-dude]

serde_macros is being deprecated in favor of serde_derive[0].
As a result, rustfix does not build on nighlty anymore[1].
This commit replaces serde_macros by serde_derive.

[0]
https://users.rust-lang.org/t/serde-transitioning-to-macros-1-1/7437/5

[1] serde-rs/serde#606 (comment)

Unfortunately, this is not enough:

error[E0277]: the trait bound `rustfix::diagnostics::Diagnostic: serde::de::Deserialize` is not satisfied
  --> src/main.rs:78:26
   |
78 |         .flat_map(|line| serde_json::from_str::<Diagnostic>(line))
   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `serde::de::Deserialize` is not implemented for `rustfix::diagnostics::Diagnostic`
   |
   = note: required by `serde_json::from_str`

I dont' get this error because rustfix::diagnostics::Diagnostic does derive Deserialize: https://github.com/killercup/rustfix/blob/master/src/diagnostics.rs#L5

Feel free to close in favor of a working PR, otherwise, I'll try to finish this tonight.

[killercup]

Thanks! I think you only need minimal changes to make this work :)

You need to load serde_derive and enable the new macro feature. Reading https://serde.rs/codegen.html, I think you just need to replace the first few lines in lib.rs with this:

#![feature(proc_macro)]

#[macro_use]
extern crate serde_derive;

extern crate serde_json;

If you want to, you can also try to make this compile on stable Rust (as a different PR maybe).

By the way, can you also change the nightly's date to a more recent one in .travis.yml?

[little-dude]

Thank you for your help! It now builds on the latest nightly:

$ rustc --version
rustc 1.14.0-nightly (cae6ab1c4 2016-11-05)

[killercup]

Thanks again!