Switched to official rust image for gitlab ci

1 job for <span class="ref-name">part-3</span> in 2 minutes and 52 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
failed #46965917
test:cargo

00:02:52

 
Name Stage Failure
failed
test:cargo Test There is an unknown failure, please try again

$ cargo +nightly install rustfmt-nightly
Updating registry `https://github.com/rust-lang/crates.io-index`
Downloading rustfmt-nightly v0.3.4
Installing rustfmt-nightly v0.3.4
error: binary `cargo-fmt` already exists in destination
binary `rustfmt` already exists in destination
Add --force to overwrite
ERROR: Job failed: exit code 1