This fixes UI tests on Linux nightly. Without the `rust-src` component,
an error message pointing to the core libraries is not emitted as
expected. Presumably by making the sources available, the compiler has
somewhere to point to.
This commit also re-enables CI failures for the Linux debug target.
This allows us to test all of the "core" crates (and the guide) by
testing the root workspace, and all of the examples by testing in the
examples workspace.
To the Rust teams, Rust's contributors, Rocket's contributors, the
entire Rust and Rocket communities, my colleagues at Stanford and
beyond, and Jeb: thank you all. Sincerely.
To the next ~4 years of Rocket!
Closes#19.