Don't download an extra toolchain on appveyor

Author: brson

appveyor.yml

@@ -22,9 +22,8 @@ install:
   # Install rust, x86_64-pc-windows-msvc host
   # FIXME: switch back to win.rustup.rs
   - curl -sSf -o rustup-init.exe https://dev-static.rust-lang.org/rustup/dist/i686-pc-windows-gnu/rustup-init.exe
-  - rustup-init.exe -y
+  - rustup-init.exe -y --default-toolchain=nightly-2016-08-10-x86_64-pc-windows-msvc
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
-  - rustup default nightly-2016-08-10-x86_64-pc-windows-msvc
 
   # Install the target we're compiling for
   - if NOT "%TARGET%" == "x86_64-pc-windows-msvc" rustup target add %TARGET%