upgrade ruby

appveyor.yml

@@ -8,7 +8,7 @@ branches:
 
 install:
   - git submodule update --init --recursive
-  - set PATH=C:\Ruby22\bin;%PATH%
+  - set PATH=C:\Ruby23\bin;%PATH%
   - git config core.symlinks true
   - git reset --hard
   - cd docs