Test on JRuby 9.4

Author: janko

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
           - "3.0"
           - "3.1"
           - "3.2"
-          - "jruby-9.2"
+          - "jruby-9.4"
 
     steps:
       - uses: actions/checkout@v2