Build on x64 on AppVeyor but compile for x86 as well

appveyor.yml

@@ -1,19 +1,24 @@
 os: Visual Studio 2015
 
+platform: x64
+
 environment:
   NODEJS_VERSION: "6"
+  matrix:
+    - node_arch: x64
+      rust_toolchain: stable-x86_64-pc-windows-msvc
 
-platform:
-  - x86
-  - x64
+    - node_arch: x86
+      rust_toolchain: stable-i686-pc-windows-msvc
 
 install:
   - ps: Install-Product node $env:NODEJS_VERSION $env:PLATFORM
   - node -e "console.log(process.arch, process.versions)"
 
   - curl -sSf -o rustup-init.exe https://win.rustup.rs
-  - rustup-init.exe -y
+  - rustup-init.exe --no-prompt --default-toolchain %rust_toolchain%
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
+  - rustup show
   - rustc -V
   - cargo -V