appveyor: use rustup

appveyor.yml

@@ -4,9 +4,9 @@ environment:
     - TARGET: x86_64-pc-windows-msvc
 
 install:
-  - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-nightly-${env:TARGET}.exe"
-  - rust-nightly-%TARGET%.exe /VERYSILENT /NORESTART /DIR="C:\Program Files (x86)\Rust"
-  - SET PATH=%PATH%;C:\Program Files (x86)\Rust\bin
+  - curl -sSf -o rustup-init.exe https://win.rustup.rs
+  - rustup-init.exe --default-host %TARGET% --default-toolchain nightly -y
+  - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
   - gem install gist
   - rustc -Vv
   - cargo -V