Lost a feature

[dannypsnl]

--> .../.cargo/.../json-0.11.9/src/value/mod.rs:369:5
|
369 | #[must_use]
| ^^^^^^^^^^^
|
= help: add #![feature(fn_must_use)] to the crate attributes to enable
After add this line into the file, it really be fixed.

[dannypsnl]

Seems already had the same problem at issue #119 .