Update appveyor config

appveyor.yml

@@ -7,20 +7,29 @@ environment:
         - RUST_INSTALL_TRIPLE: x86_64-pc-windows-msvc
           RUST_CHANNEL: nightly
 
+matrix:
+    allow_failures:
+        - RUST_CHANNEL: nightly
+
 install:
     - ps: Start-FileDownload "http://static.rust-lang.org/dist/channel-rust-${env:RUST_CHANNEL}"
     - ps: $env:RUST_INSTALLER = Select-String "${env:RUST_INSTALL_TRIPLE}.*exe" "channel-rust-${env:RUST_CHANNEL}" | select -exp line
     - ps: Start-FileDownload "http://static.rust-lang.org/dist/${env:RUST_INSTALLER}"
     - '%RUST_INSTALLER% /VERYSILENT /NORESTART /DIR="C:\Rust"'
     - call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" amd64
-    - ps: Invoke-WebRequest -UserAgent wget -Uri "http://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Personal%20Builds/mingw-builds/5.1.0/threads-win32/seh/x86_64-5.1.0-release-win32-seh-rt_v4-rev0.7z/download" -OutFile mingw64.7z
-    - ps: 7z x -oC:\ mingw64.7z > $null
-    - ps: $env:path = "C:\mingw64\bin;C:\Rust\bin;" + $env:path
-    - gcc --version
+    - ps: $env:path = "C:\Rust\bin;" + $env:path
+    - ps: |
+        if ($env:RUST_INSTALL_TRIPLE -like "*-gnu") {
+            Start-FileDownload "http://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Personal%20Builds/mingw-builds/5.1.0/threads-win32/seh/x86_64-5.1.0-release-win32-seh-rt_v4-rev0.7z/download" -FileName mingw64.7z
+            7z x -oC:\ mingw64.7z > $null
+            $env:path = "C:\mingw64\bin;" + $env:path
+            gcc --version
+        }
     - rustc --version --verbose
     - cargo --version
 
 build: false
 
 test_script:
+    - cargo build
     - cargo test