[CI] Update rust format version

[tqchen]

cc @nhynes @ehsanmok

The update the rust docker creates outrage in the CI because of version mismatch. Next time, we might need to consider a safe transition rule(e.g. remove test or relax version for now)

[ehsanmok]

You are right! Thanks for the update. The docker install rustfmt version must match exactly with the version used in .rustfmt.

[nhynes]

This is a giant problem with rustfmt. Fortunately we've finally made it to stable nightly (whatever that means) so it'll be quite a while before we update again. At most in 3 years when rust releases another edition.

[tqchen]

@nhynes can u comment on http://ci.tvm.ai:8080/blue/organizations/jenkins/tvm/detail/PR-2550/3/pipeline? If there is a quick fix to this problem

[ehsanmok]

@tqchen That's a new rustfmt rule. Please change make those #![allow(...)] in rust/src/lib.rs in one line:

#![allow(non_camel_case_types, non_snake_case, non_upper_case_globals, unused)]

I verified it locally on rustc 1.34.0-nightly (852701ad6 2019-02-01). However, cargo build gives 5 warnings including

use of deprecated item 'std::sync::atomic::ATOMIC_USIZE_INIT': the `new` function is now preferred`

that should be fixed in frontend merge.

[ehsanmok]

Hopefully as Nick said, we won't get headache after this. The lesson was such changes should be verified independent from current docker setup then commit the changes all at once in docker and rustfmt config.

[tqchen]

OK, I temporarily disabled the rust test in tests/task_rust.sh, please send in another PR to fix the files and re-enable the tests(or update the frontend test)