Add ruby 3 support

Author: rmm5t

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: [2.4, 2.5, 2.6, 2.7]
+        ruby: [2.4, 2.5, 2.6, 2.7, 3.0, 3.1]
 
     steps:
       # https://github.com/marketplace/actions/checkout