Fix nightly compilation

[Xanewok]

Bumps rustfmt-nightly to 0.3.5.

[Xanewok]

cc rust-lang/rust#47454

r? @nrc

[Xanewok]

What's worrying is that RUSTFMT=false Linux job fails integration tests:

thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 32, kind: BrokenPipe, message: "Broken pipe" }', libcore/result.rs:916:5
test test_simple_workspace has been running for over 60 seconds
test test_infer_bin has been running for over 60 seconds
test test_infer_bin ... FAILED
test test_simple_workspace ... FAILED

This may be unrelated, however I certainly hope intermittent test failures are not at it again... 😨

[nrc]

Thanks!