update appveyor allowed bundler versions

Author: JonRowe

travis/appveyor.yml

@@ -15,7 +15,7 @@ install:
   - SET PATH=C:\Ruby%ruby_version%\bin;%PATH%
   - ruby --version
   - gem --version
-  - gem install bundler
+  - gem install bundler -v "!= 1.12.0, != 1.12.1, != 1.12.2, != 1.12.3"
   - bundler --version
   - bundle install
   - cinst ansicon