appveyor.yml in html2doc-0.8.12 vs appveyor.yml in html2doc-0.8.13

@@ -5,10 +5,11 @@
 cache:
   - vendor/bundle
 
 environment:
   matrix:
+    - RUBY_VERSION: 26
     - RUBY_VERSION: 25
     - RUBY_VERSION: 24
     - RUBY_VERSION: _trunk
 
 matrix:
@@ -20,9 +21,10 @@
   - refreshenv
 
 build_script:
   - set PATH=C:\Ruby%RUBY_VERSION%\bin;%PATH%
   - set GIT_TERMINAL_PROMPT=0
+  - gem install bundler -v "~> 2"
   - bundle config --local path vendor/bundle
   - bundle update
   - bundle install
 
 before_test: