ci(appveyor): add windows testing (#1468)

* ci(appveyor): init windows testing

* squash(test): ...

Author: michael-ciniawsky

appveyor.yml

@@ -0,0 +1,27 @@
+build: 'off'
+
+init:
+  - git config --global core.autocrlf input
+
+environment:
+  matrix:
+    - nodejs_version: '10'
+      webpack_version: latest
+    - nodejs_version: '8'
+      webpack_version: latest
+    - nodejs_version: '6'
+      webpack_version: latest
+
+matrix:
+  fast_finish: true
+
+install:
+  - ps: Install-Product node $env:nodejs_version x64
+  - npm i -g npm@latest
+  - npm i
+
+before_test:
+  - cmd: npm i webpack@%webpack_version%
+
+test_script:
+  - cmd: npm t