Use latest Julia and Ruby versions on CI

Author: mrkn

.github/workflows/ci.yml

@@ -23,19 +23,13 @@ jobs:
  - macos-10.15
  # - windows-latest
  julia:
- - 1.5
+ - 1.8
+ - 1.6
  ruby:
+ - "3.1"
  - "3.0"
  - 2.7
- - 2.6
- - 2.5
  - debug
- include:
- # - { os: windows-latest , julia: 1.5 , ruby: mingw }
- # - { os: windows-latest , julia: 1.5 , ruby: mswin }
- - { os: ubuntu-20.04 , julia: 1.6-rc1 , ruby: "3.0" }
- #exclude:
- # - { os: windows-latest , julia: 1.5 , ruby: debug }
 
  steps:
  - uses: actions/checkout@v2