Upgrade to Ruby 2.5.3

Attempt to update google-protobuf for migration-paths

Because the one we were using aren't compatible with
Ruby 2.5.3, and it'll be troublesome to switch Ruby.
Upgrading google-protobuf will be much easier.

All of them will need to be updated for Ruby 2.5.3

We remove oj because we don't really need it and it
doesn't compile on 2.5.3 with that version.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/41825

.gitlab-ci.yml

-image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.4.5-golang-1.9-git-2.18-chrome-69.0-node-10.x-yarn-1.12-postgresql-9.6-graphicsmagick-1.3.29"
+image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-golang-1.9-git-2.18-chrome-69.0-node-10.x-yarn-1.12-postgresql-9.6-graphicsmagick-1.3.29"
 
 .dedicated-runner: &dedicated-runner
   retry: 1
@@ -6,7 +6,7 @@ image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.4.5-golang-1.9-git
     - gitlab-org
 
 .default-cache: &default-cache
-  key: "debian-stretch-ruby-2.4.5-node-10.x"
+  key: "debian-stretch-ruby-2.5.3-node-10.x"
   paths:
     - vendor/ruby
     - .yarn-cache/
@@ -152,7 +152,7 @@ stages:
   <<: *except-docs-and-qa
 
 .single-script-job: &single-script-job
-  image: ruby:2.4-alpine
+  image: ruby:2.5-alpine
   stage: test
   cache: {}
   dependencies: []
@@ -316,6 +316,8 @@ stages:
   script:
     - git fetch https://gitlab.com/gitlab-org/gitlab-ee.git v9.3.0-ee
     - git checkout -f FETCH_HEAD
+    - sed -i "s/gem 'oj', '~> 2.17.4'//" Gemfile
+    - bundle update google-protobuf grpc
     - bundle install $BUNDLE_INSTALL_FLAGS
     - date
     - cp config/gitlab.yml.example config/gitlab.yml
@@ -423,7 +425,7 @@ review-docs-cleanup:
 # Trigger a docker image build in CNG (Cloud Native GitLab) repository
 #
 cloud-native-image:
-  image: ruby:2.4-alpine
+  image: ruby:2.5-alpine
   before_script: []
   dependencies: []
   stage: test
@@ -506,7 +508,7 @@ update-tests-metadata:
 
 flaky-examples-check:
   <<: *dedicated-runner
-  image: ruby:2.4-alpine
+  image: ruby:2.5-alpine
   services: []
   before_script: []
   variables:
@@ -754,7 +756,7 @@ static-analysis:
   script:
     - scripts/static-analysis
   cache:
-    key: "debian-stretch-ruby-2.4.5-node-10.x-and-rubocop"
+    key: "debian-stretch-ruby-2.5.3-node-10.x-and-rubocop"
     paths:
       - vendor/ruby
       - .yarn-cache/
@@ -878,7 +880,7 @@ gitlab:setup-mysql:
 # Frontend-related jobs
 gitlab:assets:compile:
   <<: *dedicated-no-docs-and-no-qa-pull-cache-job
-  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.4.4-git-2.18-chrome-69.0-node-8.x-yarn-1.2-graphicsmagick-1.3.29-docker-18.06.1
+  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-git-2.18-chrome-69.0-node-8.x-yarn-1.2-graphicsmagick-1.3.29-docker-18.06.1
   dependencies: []
   services:
     - docker:stable-dind

.ruby-version

-2.4.5
+2.5.3