Update Rust toolchain to nightly-2020-01-08

[soc]

No description provided.

[dinfuehr]

Do you know why the tests seem to fail?

[soc]

The test fails with

error: include macro expected single expression in source
##[error]  --> /Users/runner/runners/2.163.1/work/dora/dora/target/debug/build/dora-8a7f4f335047c02d/out/dora_stdlib_bundle.rs:31:2
   |
31 | ];
   |  ^
   |
   = note: `#[deny(incomplete_include)]` on by default

I assume that the rules for include macro have changed, seems to be rust-lang/rust#64284. What shall we do about it?

EDIT: I'm on it, updated commit incoming.

[soc]

Should be fixed now.