Merge pull request #93 from evolve75/coverall-check-on-3.1

`Coveralls` test coverage check on Ruby 3.1.

Author: evolve75

.github/workflows/coveralls.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ["2.6", "2.7", "3.0"]
+        ruby: ["2.6", "2.7", "3.0", "3.1"]
     runs-on: ubuntu-latest
 
     steps: