Add Ruby 2.3 to AppVeyor matrix

Author: sodabrew

appveyor.yml

@@ -25,6 +25,8 @@ test_script:
 #  - find tmp -name "*.log" -exec cat {};
 environment:
   matrix:
+    - ruby_version: "23-x64"
+    - ruby_version: "23"
     - ruby_version: "22-x64"
     - ruby_version: "22"
     - ruby_version: "21-x64"