Bump JRuby 9.2 test image to 9.2.20.1 (latest) release

While investigating another JRuby issue (see #1840) I upgraded the
`ethon` gem and ran into a new issue --
typhoeus/ethon#205 .

That `ethon`issue is actually a JRuby bug, and has been fixed in the
latest versions of JRuby 9.2, so instead of adding
yet-another workaround to our Appraisals, let's just upgrade the
JRuby image we use for testing :)

While I was in the neighbourhood, I also bumped the resource class
for JRuby 9.2 testing in CI, to hopefully reduce the time it takes
to run CI with JRuby by giving it a bit more oomph.

.circleci/config.yml

@@ -499,7 +499,8 @@ job_configuration:
   - &config-jruby-9_2-latest # More recent release of 9.2
     <<: *filters_all_branches_and_tags
     ruby_version: 'jruby-9.2-latest'
-    image: ivoanjo/docker-library:ddtrace_rb_jruby_9_2_18_0
+    image: ivoanjo/docker-library:ddtrace_rb_jruby_9_2_20_1
+    resource_class_to_use: medium+
   # TruffleRuby
   - &config-truffleruby-21_0_0
     <<: *filters_all_branches_and_tags

.circleci/images/primary/Dockerfile-jruby-9.2-latest

@@ -1,5 +1,5 @@
-# https://hub.docker.com/layers/jruby/library/jruby/9.2.18-jre8/images/sha256-8dd56d26850fbba5c558fe195f98f2cc765d82e91ace601e3fc2273c1f9c95b5
-FROM jruby@sha256:8dd56d26850fbba5c558fe195f98f2cc765d82e91ace601e3fc2273c1f9c95b5
+# https://hub.docker.com/layers/jruby/library/jruby/9.2.20.1-jdk8/images/sha256-d270305f8ddb6625b6651947234eb69685d17bb0511c0964936ebece6af450f5
+FROM jruby@sha256:d270305f8ddb6625b6651947234eb69685d17bb0511c0964936ebece6af450f5
 
 # Make apt non-interactive
 RUN echo 'APT::Get::Assume-Yes "true";' > /etc/apt/apt.conf.d/90circleci \

docker-compose.yml

@@ -308,7 +308,7 @@ services:
       - bundle-jruby-9.2.0.0:/usr/local/bundle
       - "ddagent_var_run:${TEST_DDAGENT_VAR_RUN}"
   tracer-jruby-9.2-latest:
-    image: ivoanjo/docker-library:ddtrace_rb_jruby_9_2_18_0
+    image: ivoanjo/docker-library:ddtrace_rb_jruby_9_2_20_1
     command: /bin/bash
     depends_on:
       - ddagent