[Tests] [appveyor] drop support for pre-node-4, add node 6.

Author: ljharb

appveyor.yml

@@ -1,10 +1,8 @@
 environment:
   matrix:
-    - nodejs_version: '0.10'
-    - nodejs_version: '0.12'
-    - nodejs_version: '3'
     - nodejs_version: '4'
     - nodejs_version: '5'
+    - nodejs_version: '6'
 install:
   - ps: Install-Product node $env:nodejs_version
   - set CI=true