Update ruby.yml

Author: wenbinf

.github/workflows/ruby.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.5', '2.6', '2.7', '3.0']
+        ruby-version: ['2.3', '2.5', '2.6', '2.7', '3.0']
 
     steps:
     - uses: actions/checkout@v2