AppVeyor: test only on io.js 3

More versions are tested on Travis.

Author: mgol

appveyor.yml

@@ -9,10 +9,7 @@ init:
 # Test against these versions of Node.js.
 environment:
   matrix:
-    # Node.js
-    - nodejs_version: "0.12"
-    # io.js
-    - nodejs_version: "2"
+    - nodejs_version: "3"
 
 # Install scripts. (runs after repo cloning)
 install:
@@ -38,8 +35,6 @@ build: off
 # Finish immediately if one of the jobs fails.
 matrix:
   fast_finish: true
-  allow_failures:
-    - nodejs_version: "2"
 
 # Set up cache, clear it on package.json changes.
 cache: