Update Rust compiler to latest stable (1.43.1)

[gpestana]

Description

The cxx crate, which can be used to avoid using unsafe Rust code in FFIs, requires that the rustc compiler version is 1.42+ . Updating the current Rust toolchain (which uses rustc 1.41) would allow us to use it.

Steps to Reproduce

RUSTUP_HOME=build/rustup/0.1.2 rustc -V

Actual result:

1.41.2

Expected result:

rustc 1.42.0 (b8cedc004 2020-03-09)

Reproduces how often:

Always