CI fails with `unresolved import `self::std::hint`

[jeehoonkang]

https://travis-ci.org/crossbeam-rs/crossbeam/jobs/577310627#L270

I checked in my local machine that it happens in the current master for Rust 1.26.0.

[Vtec234]

Do we still support 1.26.0?
This is due to a change in lazy_static, where version 1.3.0 still works but 1.4.0 doesn't. The oldest rustc supported by 1.4.0 is 1.27.2, while for 1.3.0 it was 1.24.1.