Do not specify ruby version of macOS

hsbt · hsbt · commit 77448726bb05 · 2019-02-26T21:09:48.000+09:00
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
@@ -25,9 +25,6 @@ jobs:
   pool:
     vmImage: 'macos-10.13'
   steps:
-  - task: UseRubyVersion@0
-    inputs:
-      versionSpec: '>= 2.4'
   - script: |
       gem install bundler
       bundle install --retry=3 --jobs=4
