rustup-init.exe: Update Visual Studio C++ build tools

[mcandre]

Could we update the rustup-init.exe installer for Windows? It recommends that users install an older set of build tools, the 2015 ones, whereas Microsoft has since released a 2017 set of build tools.

[mattico]

The repo for rustup is over here: https://github.com/rust-lang-nursery/rustup.rs

As to your suggestion, I'd probably wait to update the message until the 2017 build tools are supported by rust stable. The support for them was added recently, I think they'll be in 1.20.0

[steveklabnik]

That's all correct. Thanks!