Update JRuby to 9.3 to support Ruby 2.6 syntax

Author: p0deje

.github/workflows/ruby.yml

@@ -143,7 +143,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['2.6', 'jruby-9.2.19.0']
+        ruby: ['2.6', 'jruby-9.3.0.0']
     steps:
       - uses: actions/checkout@v2
       - uses: ruby/setup-ruby@v1