appveyor: drop node v2 and v3

Author: TooTallNate

appveyor.yml

@@ -10,8 +10,6 @@ environment:
     - nodejs_version: "0.10"
     - nodejs_version: "0.12"
     # io.js
-    - nodejs_version: "2"
-    - nodejs_version: "3.2"
     - nodejs_version: "4"
     - nodejs_version: "5"
     - nodejs_version: "6"