Update JRuby on Travis to avoid rubygems bug

> Your RubyGems version (3.1.6)) has a bug that prevents `required_ruby_version` from working for Bundler. Any scripts that use `gem install bundler` will break as soon as Bundler drops support for your Ruby version. Please upgrade RubyGems to avoid future breakage and silence this warning by running `gem update --system 3.2.3`

.travis.yml

@@ -18,6 +18,8 @@ matrix:
     - rvm: 2.7.3
     - rvm: 3.0.1
     - rvm: jruby-9.2.17.0
+      before_install:
+        - yes | gem update --system
       env:
         - JRUBY_OPTS="--debug"
     - rvm: truffleruby-head