Add node versions 4, 6, 8, 10, 12 to Appveyor

Author: andreas

appveyor.yml

@@ -16,6 +16,16 @@ environment:
     nodejs_arch: "x86"
   - nodejs_version: "2"
     nodejs_arch: "x64"
+  - nodejs_version: "4"
+    nodejs_arch: "x64"
+  - nodejs_version: "6"
+    nodejs_arch: "x64"
+  - nodejs_version: "8"
+    nodejs_arch: "x64"
+  - nodejs_version: "10"
+    nodejs_arch: "x64"
+  - nodejs_version: "12"
+    nodejs_arch: "x64"
 install:
   - ps: Install-Product node $env:nodejs_version $env:nodejs_arch
   - npm install --msvs_version=2013