Update appveyor.yml to test against node 12.13.1

Author: baparham

appveyor.yml

@@ -1,13 +1,13 @@
 # Test against this version of Node.js
 environment:
-  nodejs_version: "4.1.2"
+  nodejs_version: "12.13.1"
 
 # Install scripts. (runs after repo cloning)
 install:
   # Get the latest stable version of Node.js or io.js
   - ps: Install-Product node $env:nodejs_version
   # Upgrade npm
-  - npm install -g npm@3
+  - npm install -g npm@6
   # install modules
   - npm install
   - npm install grunt-cli -g