Test Ruby 3.0 on CI

Author: odlp

.github/workflows/main.yml

@@ -6,7 +6,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.7, 2.6, 2.5]
+        ruby: [3.0, 2.7, 2.6, 2.5]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2