Remove Ruby 2.5

Author: shugo

.github/workflows/ubuntu.yml

@@ -6,7 +6,7 @@ jobs:
   test:
     strategy:
       matrix:
-        ruby: [ head, 3.1, 2.7, 2.6, 2.5 ]
+        ruby: [ head, 3.1, 2.7, 2.6 ]
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2