add appveyor config (#280)

Author: shellscape

appveyor.yml

@@ -0,0 +1,24 @@
+
+init:
+  - git config --global core.autocrlf input
+environment:
+  matrix:
+    - nodejs_version: '9'
+      webpack_version: latest
+    - nodejs_version: '8'
+      webpack_version: latest
+    - nodejs_version: '6'
+      webpack_version: latest
+build: 'off'
+matrix:
+  fast_finish: true
+install:
+  - ps: Install-Product node $env:nodejs_version x64
+  - npm i -g npm@latest
+  - npm install
+before_test:
+  - cmd: npm install webpack@%webpack_version%
+test_script:
+  - node --version
+  - npm --version
+  - cmd: npm run ci