Update to node@12

This updates our build images to use node@12. We are also adding a
sentence to the from-source installation that while we require a minimum
version of node@8, we also recommend node@12. Last but not least, we
change the version of node in the .nvmrc so that developers using nvm
can automatically use node@12 with the project

.gitlab/ci/frontend.gitlab-ci.yml

@@ -16,7 +16,7 @@
 gitlab:assets:compile:
   <<: *assets-compile-cache
   extends: .dedicated-no-docs-pull-cache-job
-  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.6.3-git-2.21-chrome-73.0-node-8.x-yarn-1.12-graphicsmagick-1.3.29-docker-18.06.1
+  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.6.3-git-2.21-chrome-73.0-node-12.x-yarn-1.16-graphicsmagick-1.3.29-docker-18.06.1
   dependencies:
     - setup-test-env
   services:

.gitlab/ci/global.gitlab-ci.yml

@@ -9,7 +9,7 @@
     - gitlab-org
 
 .default-cache: &default-cache
-  key: "debian-stretch-ruby-2.6.3-node-10.x"
+  key: "debian-stretch-ruby-2.6.3-node-12.x"
   paths:
     - vendor/ruby
     - .yarn-cache/

.gitlab/ci/rails.gitlab-ci.yml

@@ -92,7 +92,7 @@
 .rspec-metadata-pg-10: &rspec-metadata-pg-10
   <<: *rspec-metadata
   <<: *use-pg-10
-  image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.6.3-golang-1.11-git-2.21-chrome-73.0-node-10.x-yarn-1.12-postgresql-10-graphicsmagick-1.3.29"
+  image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.6.3-golang-1.11-git-2.21-chrome-73.0-node-12.x-yarn-1.16-postgresql-10-graphicsmagick-1.3.29"
 
 .rspec-metadata-mysql: &rspec-metadata-mysql
   <<: *rspec-metadata
@@ -240,7 +240,7 @@ static-analysis:
   script:
     - scripts/static-analysis
   cache:
-    key: "debian-stretch-ruby-2.6.3-node-10.x-and-rubocop"
+    key: "debian-stretch-ruby-2.6.3-node-12.x-and-rubocop"
     paths:
       - vendor/ruby
       - .yarn-cache/

.nvmrc

@@ -1 +1 @@
-10.13.0
+12.4.0

doc/install/installation.md

@@ -263,7 +263,7 @@ Since GitLab 8.17, GitLab requires the use of Node to compile JavaScript
 assets, and Yarn to manage JavaScript dependencies. The current minimum
 requirements for these are:
 
-- `node` >= v8.10.0.
+- `node` >= v8.10.0. (We recommend node 12.x as it is faster)
 - `yarn` >= v1.10.0.
 
 In many distros,
@@ -271,8 +271,8 @@ the versions provided by the official package repositories are out of date, so
 we'll need to install through the following commands:
 
 ```sh
-# install node v8.x
-curl --location https://deb.nodesource.com/setup_8.x | sudo bash -
+# install node v12.x
+curl --location https://deb.nodesource.com/setup_12.x | sudo bash -
 sudo apt-get install -y nodejs
 
 curl --silent --show-error https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
@@ -493,7 +493,7 @@ sudo -u git -H editor config/resque.yml
 ```
 
 CAUTION: **Caution:**
-Make sure to edit both `gitlab.yml` and `unicorn.rb` to match your setup. 
+Make sure to edit both `gitlab.yml` and `unicorn.rb` to match your setup.
 If you want to use Puma web server, see [Using Puma](#using-puma) for the additional steps.
 
 NOTE: **Note:**