Rev json gem (#62987)

dev/ci/docker_linux/Dockerfile

diff --git a/dev/ci/docker_linux/Dockerfile b/dev/ci/docker_linux/Dockerfile
index da119ba..9cfd321 100644
--- a/dev/ci/docker_linux/Dockerfile
+++ b/dev/ci/docker_linux/Dockerfile
@@ -10,6 +10,8 @@
 # for performing pushes to production, and so this image is quite a bit larger
 # than strictly needed for just building Flutter apps.
 
+# Last manual update 2020-08-05 (changing this comment will re-build image)
+
 # Note: updating past stretch (Debian 9) will bump Java past version 8,
 # which will break the Android SDK.
 FROM debian:stretch
@@ -123,7 +125,6 @@
   bundle install --system
 
 # Install goldctl, for Golden testing
-# Last updated 2020-02-04 (update to rebuild Dockerfile with latest goldctl)
 COPY bots/download_goldctl.sh /download_goldctl.sh
 ENV GOLDCTL '/depot_tools/goldctl'
 RUN /download_goldctl.sh

dev/ci/docker_linux/Gemfile.lock

diff --git a/dev/ci/docker_linux/Gemfile.lock b/dev/ci/docker_linux/Gemfile.lock
index f21f85d..f7d5092 100644
--- a/dev/ci/docker_linux/Gemfile.lock
+++ b/dev/ci/docker_linux/Gemfile.lock
@@ -93,7 +93,7 @@
     http-cookie (1.0.3)
       domain_name (~> 0.5)
     httpclient (2.8.3)
-    json (2.2.0)
+    json (2.3.1)
     jwt (2.1.0)
     memoist (0.16.0)
     mime-types (3.3)

dev/ci/mac/Gemfile.lock

diff --git a/dev/ci/mac/Gemfile.lock b/dev/ci/mac/Gemfile.lock
index 3a010b3..4fa7b13 100644
--- a/dev/ci/mac/Gemfile.lock
+++ b/dev/ci/mac/Gemfile.lock
@@ -142,7 +142,7 @@
     httpclient (2.8.3)
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
-    json (2.2.0)
+    json (2.3.1)
     jwt (2.1.0)
     memoist (0.16.0)
     mime-types (3.3)