appveyor.yml in omnibus-5.5.0 vs appveyor.yml in omnibus-5.6.0

@@ -4,11 +4,11 @@
 platform:
   - x64
 
 environment:
   matrix:
+    - RUBY_VERSION: 23
     - RUBY_VERSION: 22
-    - RUBY_VERSION: 21
 
 clone_folder: c:\projects\omnibus
 clone_depth: 1
 skip_tags: true
 branches: