install npm3 for every platform

fix issue nodejs/node-gyp#972

Author: pierreinglebert

appveyor.yml

@@ -30,10 +30,8 @@ install:
   - ps: Install-Product node $env:nodejs_version $env:platform
   # Install newer npm for node.js 0.10
   - ps: >-
-      if ($env:nodejs_version -eq "0.10") {
-        npm install -g npm@3
-        $env:PATH="$env:APPDATA\npm;$env:PATH"
-      }
+      npm install -g npm@3
+      $env:PATH="$env:APPDATA\npm;$env:PATH"
   # Add local node-pre-gyp dir to path
   - SET PATH=node_modules\.bin;%PATH%
   # Use 64-bit Python if platform is 64-bit