Use npm3

lgeiger · lgeiger · commit 6c522bab78e9 · 2016-09-28T13:38:05.000+02:00
nodejs/node-gyp#972
diff --git a/appveyor.yml b/appveyor.yml
@@ -12,6 +12,7 @@ platform:
 
 install:
   - ps: Install-Product node $env:nodejs_version $env:platform
+  - npm install -g npm@3
   - npm install
 
 test_script:
