Error compiling

[nkh]

How does one enable support for the '?' operator used since 783a...

rustc --version: rustc 1.12.1 (d4f39402a 2016-10-19)

error: the ? operator is not stable (see issue #31436)
--> src/tokenizer/mod.rs:158:44
|
158 | let argument = Number::new(number, token).into_argument(path)?;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 52 previous errors

error: Could not compile parallel.

[mmstick]

It was made stable with Rust 1.13