CI against JRuby 9.3

JRuby 9.3 has been released.
https://www.jruby.org/2021/09/22/jruby-9-3-0-0.html

```consle
% rbenv local jruby-9.3.0.0
% ruby -v
jruby 9.3.0.0 (2.6.8) 2021-09-17 85c20e780f Java HotSpot(TM) 64-Bit
Server VM 25.271-b09 on 1.8.0_271-b09 +jit [darwin-x86_64]
```

JRuby 9.3 is Ruby 2.6 compatible and RuboCop supports Ruby 2.5,
so I think RuboCop can support JRuby 9.2.

On the other hand, this PR drops JRuby 9.2 from the CI matrix.
This is a balance between increasing CI running time and issue detection.
In fact, JRuby support could be 9.3 or higher next year (2022).

https://docs.rubocop.org/rubocop/1.22/compatibility.html

.circleci/config.yml

@@ -161,26 +161,26 @@ jobs:
     steps:
       *rubocop_steps
 
-  # JRuby 9.2
-  jruby-9.2-spec:
+  # JRuby 9.3
+  jruby-9.3-spec:
     docker:
-      - image: circleci/jruby:9.2
+      - image: circleci/jruby:9.3
     environment:
       <<: *common_env
       <<: *jruby_env
     steps:
       *spec_steps
-  jruby-9.2-ascii_spec:
+  jruby-9.3-ascii_spec:
     docker:
-      - image: circleci/jruby:9.2
+      - image: circleci/jruby:9.3
     environment:
       <<: *common_env
       <<: *jruby_env
     steps:
       *ascii_spec_steps
-  jruby-9.2-rubocop:
+  jruby-9.3-rubocop:
     docker:
-      - image: circleci/jruby:9.2
+      - image: circleci/jruby:9.3
     environment:
       <<: *common_env
       <<: *jruby_env
@@ -266,16 +266,16 @@ workflows:
             - cc-setup
       - ruby-head-ascii_spec
       - ruby-head-rubocop
-      - jruby-9.2-spec:
+      - jruby-9.3-spec:
           requires:
             - cc-setup
-      - jruby-9.2-ascii_spec
-      - jruby-9.2-rubocop
+      - jruby-9.3-ascii_spec
+      - jruby-9.3-rubocop
 
       - cc-upload-coverage:
           requires:
             - ruby-2.5-spec
             - ruby-2.6-spec
             - ruby-2.7-spec
             - ruby-3.0-spec
-            - jruby-9.2-spec
+            - jruby-9.3-spec

spec/spec_helper.rb

@@ -74,7 +74,7 @@
     config.filter_run_excluding broken_on: :ruby_head
   end
 
-  if %w[jruby-9.2-ascii_spec jruby-9.2-spec].include? ENV['CIRCLE_STAGE']
+  if %w[jruby-9.3-ascii_spec jruby-9.3-spec].include? ENV['CIRCLE_STAGE']
     config.filter_run_excluding broken_on: :jruby
   end
 end