Use JRuby 9.2.14.0

The latest version of JRuby, 9.2.15.0, has a bug that prevents it from calling
"racc" command.

Author: aycabta

.github/workflows/ubuntu.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: [ 'jruby-9.2', 'head', '3.0', '2.7', '2.6', '2.5', '2.4' ]
+        ruby: [ 'jruby-9.2.14.0', 'head', '3.0', '2.7', '2.6', '2.5', '2.4' ]
     steps:
     - uses: actions/checkout@master
     - name: Set up Ruby