chore(ci): update appveyor to use stable instead of nightly

.appveyor.yml

@@ -5,11 +5,12 @@ environment:
   - TARGET: x86_64-pc-windows-gnu
   - TARGET: i686-pc-windows-gnu
 install:
-  - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-nightly-${env:TARGET}.exe" -FileName "rust-nightly.exe"
-  - ps: .\rust-nightly.exe /VERYSILENT /NORESTART /DIR="C:\rust" | Out-Null
-  - ps: $env:PATH="$env:PATH;C:\rust\bin"
+  - curl -sSf -o rustup-init.exe https://win.rustup.rs/
+  - rustup-init.exe -y --default-host %TARGET%
+  - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
   - rustc -vV
   - cargo -vV
 build: false
 test_script:
-  - cargo test --verbose --no-default-features
+  - cargo build
+  - cargo test