add 3.0 to build matrix

Author: sbruhns

.github/workflows/test.yml

@@ -5,7 +5,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.2, 2.3, 2.4, 2.5, 2.6, 2.7]
+        ruby: [2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 3.0]
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2