Fix the example code in README.md by applying the following compiler …

[NAThompson]

…suggestion:

error[E0658]: procedural macros cannot be expanded to expressions (see issue #38356)
--> src/main.rs:12:38
|
12 | rocket::ignite().mount("/hello", routes![hello]).launch();
| ^^^^^^^^^^^^^^
|
= help: add #![feature(proc_macro_non_items)] to the crate attributes to enable

[NAThompson]

This appears to only show up on the very latest rustc: I reproduced with

$ rustc --version
rustc 1.31.0-nightly (fc403ad98 2018-09-30)

and a few days ago, this was not a compile error.

[SergioBenitez]

It's not rustc that's changed, it's Rocket; we're now using procedural macros for more things than before, requiring different feature gates, and we haven't updated the README or guide docs appropriately. There's a final major change I'm working on now that will fix the README as well, but I'm waiting on rust-lang/rust#52121 to land, which will change the feature gates yet again.

[NAThompson]

Ok, cools, looks like that PR will render this one irrelevant, so this is a non-issue.